I never really played play money because i found it too unrealistic but apparently the very high stakes play money games (that you actually have to work at to get to) play similarly to the lower stakes real money games. There are also some sites online that will buy play money chips for real cash although the exchange rate is something like a bazillion play money dollars for one real money dollar. The lower stakes play money games arent going to teach you an awful lot but if you do stay there then I think SnGs are much more realistic than cash games since the the craziest players tend to bust out very early. The other option if you are into tournaments is to play some freerolls and see if you can cash in those. Freerolls dont have a buyin but if you win you can win a reasonable amount.
If I were you id deposit $100 when you have some to burn, and then play the lowest stakes you can find of the game of your choice and with any luck you wont burn it anyway.