Yeah it's not cheap like the stereo caps but it's not cheap like the stereo caps. I'm inclined to agree with the idea of beefing up the wiring, don't forget to fuse if you're bypassing fusible links (common on GM stuff at least in the 80s) and a good alternator upgrade can go a long way. You may also look and see if you can get a smaller pulley like comes in the under drive kits and stick it on there to turn it faster. Probably not healthy on the bearings but hey it'll keep you in the juice longer provided your regulator/diode trio doesn't burn up.
I have a mechman alt that put down 290amps and 2 yellowtops with 2 runs of 0awg power wire running to the trunk battery and 5500~ sub amp. I know caps are bullshit but i got it for free and it was convienient to monitor voltage. Ill jist add a gauge in the dash somewhere and drop the cap.