That must be an older guide book, last I checked it was $75 one way. The best way to get there, if you are a tourist is to fly from San Juan. You save yourself the hassle of taxi, long drive, traffic and an unreliable ferry. Spend the little extra. I love Vieques and go at least twice a year, what you are looking for and the price you are looking for it at will not be easy to find. A vacation rental is a good choice, and can help with the budget, but if you stay outside of Esperanza then you will need a car. Granted Vieques has many taxi drivers and their fares are reasonable, but they will not be at your beck and call all night. Esperanza is a great small town that has several beaches within walking distance, also many restaurants, shops, a bakery, two small grocery stores plus snorkel and kayak rental. But a swimming pool, at that price, it won't happen. $250+/night for a place with a pool. You will have the ocean within a max of two blocks, you don't need a swimming pool. After many trips to Vieques the biggest tip I give is stay in Esperanza. http://www.vrbo.com/330804
As for the crime, petty theft will be your biggest problem. Don't take valuables to the beach, no electronics, never leave your house unlocked and never leave anything in a car that you don't care to loose.
A few facts I like to tell first timers, Power and water are sketchy, but will eventually come back when it goes out. Groceries are 20% or even more than the US. Chickens and horses roam around free, so there will be crowing at all hours and watch out if driving at night, the horses are free to roam even in the road. Fill up with gas when you can, because it's a small island and when the station runs out it's out till the next delivery.