The S38,S36,M88(From the E34 M5) are all quite a bit of work to fit into an E30 chassis. A V8 is one of the most simple swaps. They are generally very short so It's just a matter of custom motor mounts and drivetrain. The S38 and all other varieties are long motors. They require some very decent pounding of the firewall.
One very common swap that will leave you with plenty of power is the M or S50 series of engine from the E36 3 series.
Either way if you do your research you will find what is possible and what isn't. A v8 swap will likely run you ~$2k Depending on the motor and how much of the work you can do yourself. An M50 swap averages around ~$700 If you can do most of the work yourself.