Aaron-
Given your very limited budget, it is very unlikely that you will find a boat that meets all of your requirements. Most boats with standing headroom and a shower are going to be newer and larger than you can afford.
Not many boats in your price range are going to be capable of being a liveaboard boat. A Cape Dory 28, Alberg 30, and a few others are going to be available, in somewhat rough shape, for your price. Most will not have a pressure water system, none will have a shower, most will have some basic electrical capacity and galley for meal preparation, but I doubt any will have a toaster
oven or much in the way of shelving. Books tend to have a relatively short lifespan on an older, smaller sailboat, unless the boat is maintained impeccably.
Any boat can be a liveaboard, but a boat smaller than 26' or so, will be a very primitive existence... more like camping on the water than anything else. There are exceptions to this of course, a Flicka 20 can make a nice liveaboard, but they are rather expensive little boats.
Also, I don't believe you've budgeted sufficient funds for maintenance, upkeep, dock and marina costs. And most marinas charge an additional fee for liveaboard boats and require a minimum of $300,000 in liability insurance.
However, you may not need to have a shower on-board the boat, since if you're living at a marina, you will generally want to use the shower and toilet facilities ashore. Using the head on the boat, while at a dock, requires that you have the
holding tank pumped out occassionally.... and that can be a problem.