If you want a cheaper cartridge than the Mega-cart (which is about $100 and has all the cartridge games plus tape and cassette games plus the ram expansions) look around for hte Behr Bonz cartridge. It's simpler, only having the cartridge games, but also significantly less expensive for a great collection of the games for the Vic, a lot of which came on cartridge. Cartridge was a lot more popular on the Vic than 64 where the floppy drive really came into its own.
And yes, the first Vic's had the weak power supply but the Pet style keys that have flat tops. I have two of these. Second model have the weak power supply (two pins into the Vic) with the C64 syle keyboard where the keys are concave shaped on top. Funny these are called C64 style since they were on the Vic before the 64, but all 64s had this style. Latest models have the concave keys and the C64 style milti-pin power connector. Even though there are two keyboards, all are the same connector and interchangable.