...erm... Possible, if u're getting 2nd hand taiwanese 15 inch rims + using back your stock tyres + rubber valves + stock locknuts.

Erm... U may still be able to get a new set of 16 inch rims, but I advise u to raise ur budget a little bit to around 700 or so. The catch is, once u get ur car, go trade in ur steel rims + tyres. U might be able to get up to 1k depending on ur negotiation skills. That'll more or less cover ur rim price. Invest on better tyres, dont try cap ayam cap kambing cap lembu tyres, they're no good. Go for Falken Ziex if ur budget is low. Or u might consider the China brands as well, their tyre quality is getting better nowadays. The only drawback is the name, and u won't know if the quality is consistent throughout the lifespan of the tyres.