You may get more replies to this and the Roatan specific forum.
Sandy Bay is huge, it will depend on where you are in Sandy Bay as to how long it takes to get to West End, figure 15 minutes it may be shorter. Same thing over land from West End to West Bay it's about 15 minutes. You can also take a water taxi from West End to West Bay.
There are heaps and heaps and heaps of taxis running back and forth from West End to Coxen Hole, there's also a minibus doing the same run. Getting a cab from Sandy Bay to West Bay is not a big deal because those guys are running back and forth from West End to Coxen Hole.. it's a little bit tougher going the other way but you could grab a water taxi from West Bay to West End and then go with one of the heaps and heaps of taxis in West End, or the Mini Bus.
Getting it done is easy, but I imagine the expense adds up.