May I play reminisce? It is (somewhat) pertinent.
When Peter and I were cruising in the Caribbean, we spent the high tourist season in St. Martin and socialized with family and friends who came down. By the end of March we needed a "vacation" from all the vacationers, so we would sail over to the Virgins to "dry out" and look for crusiing friends over there. On our annual sail over, we stopped in the USVIs first. After a few days, I went to the store to get some fresh groceries. Prices were slightly higher than St. Maarten, but not alarmingly so. A week later we were in the BVIs, and I again bought some groceries. This time, the price of the small bag of groceries was very high. I didn't mean to be rude, but the price seemed impossibly higher than the provisions I had bought the week before. The poor checkout clerk then took everything out of the bag and rechecked everything. Price was still the same. I was a bit embarrassed to have put her through the extra effort and I wasted little time paying the bill and repacking the bag and getting out of there.
I know that charter prices in the Caribbean are cheaper during hurricane season, and you certainly should be able to get the pick of the charter fleet in July. The winds aren't usually as strong as in the winter, and it can be quite hot, though the water will be wonderfully right and while on the boat you won't suffer the way you would on land.
When we left Boston to go cruising, we almost got stalled in the Chesapeake. We must have spent two months there, chased out by the start of cool Fall weather and still very far from warm winter climates. What we were warned about was running aground, and we did, but it's mostly mud and easy to get off (but we had a fin keel, doesn't go as hard aground as full keel boats do.) We had a wonderful time.
I'm afraid I don't have any information on charter companies, but you should be able to get references.