If the engine and transmission run fine, then I think it is a great buy. $900 for a MR2 is a great price. Put $1200 into suspension and wheels/tires and you will have a fun little go cart. And if the motor breaks, so what, motors for that car are cheap. And if suspension parts break, so what, parts for the car are cheap and plentyful from a salvage yard.

I would check for any accessive rust, burning oil in the exhaust fumes, and any leaks that might allow water to get into the cabin. If the car does not have ttops, I would definetly get it, if it does have ttops, I would inspect carefully to see if water has leaked in through them.