Honestly, don't push the car too hard if you can't afford the maintenance, but it is possible to learn some race techniques without pushing the car too hard or even by speeding.
Also, try asking in the Pontiac Sunfire forum about what your engine trouble is about. Ignoring the problem will only make it worse. Who knows? Maybe it's something you can fix yourself.
Don't drop into D from neural while rev's are up. This is called "neutral dropping". It will damage your transmission.
If you are really serious about pushing your skills forward, look into some local AutoX events. However, doing AutoX will cost you brakes and tires. But if you ever get the money to afford it, try looking into it.