Logistics. 3 months water? And food? On a sub 30 footer? You any good at living on a gallon a day? Achievable? Yes. Easy? Not so much. Consider options. Water maker. Expensive. More port calls. Possibly costly. A cruiser with big tankage. A bonus if you pick the right one, but maybe not the least costly choice. You will want fresh food more than you might imagine once you're between somewhere and nowhere and pounding down another can of something, or reconstituted freeze-dried stuff (needs water). You're gonna wanna pull in somewhere.
Agreed, your financial targets are low. In this economic climate, you may get a great deal, but when figured with more honest methods, inflation is already around 10%, and likely to go higher, so your supplies will cost more. Definitely plan on more money.