Collectivo taxis charge per person, with the taxi being shared by various people, and drive set routes. The first route is between West End and Coxen Hole, so if you're staying in Sandy Bay, you'd take a taxi on this route. To get a taxi, you'd just go to the main road, go to the correct side of the road for the direction that you'll be heading, and lift up your hand as one is passing by. If a taxi stops for you, it's implied that it is collectivo, but if you ask too many questions and they think that you don't know about the collectivo service, then they'll quote you expresso pricing (more about that in a moment). To get the collectivo fare, just get in, and let the taxi know when to stop, get out, and pay your fare, no questions for fare confirmation needed. The set collectivo rates are only during the day, from early morning (taxis start running by about 5:30) until about 7pm. The rate at the time of writing is 30 lemp (about $1.50) per person to go from Sandy Bay to West End, and 40 lemp ($2) per person to go from Sandy Bay to Coxen Hole. In Coxen Hole, you can specify where you'd like to be dropped off (such as 'supermercado Eldons', or el mercado). If you are going somewhere along the way that is off of the main road (for example, if you want to get dropped off right outside of the hostel, because you're carrying a lot), there is a surcharge to take you there, about 5-15 lemp, depending how much off the road it is, and if you're in a taxi that has someone heading off the main road, you'll be along for the ride for this detour. If you're leaving West End, there are taxis usually waiting at the entrance to West End that want a higher expresso fare. If you'd like a collectivo taxi, just wait until there's a taxi that's departing from West End, and flag them down. In Coxen Hole, some of the taxis that are at the grocery store would like a higher expresso fare. If you'd like a collectivo taxi, check with the taxi driver, or if you don't have much to carry, walk back down to the main road to flag one down.
Coxen Hole to French Harbour is the next route. I don't know the pricing off the top of my head, but the rates will be similar (probably around 45 lemp all the way to French Harbour). The airport, even though it's just outside of Coxen Hole, is technically on this next route, so you'll have to pay for that distance as well (the minimum collectivo fare is 25 lemp, so Coxen Hole to the airport would be 25 lemp). If you're planning to go from Sandy Bay up to French Harbour or somewhere along the way (like the ferry), this is two separate routes, so to get collectivo pricing, you'd need to switch taxis in Coxen Hole. To go all the way in one taxi would be an expresso trip, and the price would need to be agreed upon with the driver before getting in.
Expresso trips are any direct taxi rides: usually you'll have the taxi to yourself, but if there was already someone in when you flagged the taxi, then they'd stay in until their drop off point. Expresso trips would be, for example, going to West Bay, going to the ferry, but could also be somewhere on the collectivo route if you just wanted to get there without picking up anyone else, or if you didn't know about the collectivo service. The same taxi provides both types of pricing. There are no meters, expresso fares should be agreed upon before getting in the taxi. Typically Sandy Bay to West Bay might be $10, for example. If you wanted an expresso trip to the ferry, but you don't mind if the driver stops for others along the way, it'll be cheaper, maybe 100 lemp ($5).
In the evening, taxi rates go up. There's still the option for a shared taxi, but there's not fixed rates, so you should agree on the pricing before getting in. The later it gets, the more expensive it is. A taxi at 9pm from West End to Sandy Bay might be 40 or 50 lemp per person, and a taxi for the same route at 1 in the morning might be 100 lemp per person (sometimes a little cheaper if there are several of you, but never back as low as daytime pricing, no matter if the taxi is completely full, as the taxi driver can be waiting a long time between fares). Even though the rates are more expensive at night, they're normally reasonable- if there's a taxi that gives a high pricing, just flag them on and wait for the next one. Taxi rates are way, way cheaper than in North America, unless you're taking an expresso taxi and haven't negotiated well (by the cruise ship ports, all the taxis want high pricing, and airport and ferry parking lots are also pretty high, usually $15-$25 to Sandy Bay: we can arrange a pick up, including a grocery store stop, for $15 when you arrive if you'd prefer).
Scooters are about $30/day, and there are several scooter rental places in West End. If renting a scooter, I'd recommend staying on the main paved road (on the dirt road at the far east end of the island, as well as the dirt road that goes out to Palmetto Bay, there have occasionally been hold-ups to people on scooters, so it's not worth the risk). Also, make sure you're driving cautiously, not overtaking on curves in the road, as scooter accidents can be very severe. That being said, it's a wonderful sensation to venture around the island on a scooter, so enjoy!
Car rentals start at about $35/day, with the cheapest options being offered from KIA, Econo and Dollar, which are all by the airport. Car rental agencies will put a freeze on a certain amount on your card (I think around $1000) to hold for any potential damages to the vehicle, so you'll need to make sure your card can support that, and there's usually a minimum age (either 21 or 25, can't remember). Sharing a car with a few other hostel guests can make renting a car a very economical way to see the island. We've got maps of Roatan at the hostell, so make sure to ask us some good spots to stop on your tour. You're welcome to leave the car parked in our driveway.
No matter how you choose to do it, get out an explore the island! Roatan is incredibly beautiful, lush and hilly, with lots of great spots to check out.