I would like to second the idea of an inflatable. I just got my second one. My first was a 12.5 foot Zodiac with a 15 hp I used it for the last 13 years for diving and just sold it for $1000. This year I replaced it with a 13.8 foot from West Marine with a 25 hp. It is definitely over your $500 but it is the most stable small boat and folds up real small. Deflated I could carry the Zodiac by my self. The new one dose require several volunteers. (Thank to all the helpers at Ocean Cove this year) If you get an inflatable I would recommend getting a good one not a cheep one.
Regards Dan H