reworking a fully restored car

Chris, I wouldn't buy a cheap spot welder to put your car together, more than likely the welds will pop loose over time leaving you with more work. It would be better to invest in a mig welder and plug weld the panels on, will be less risk of panels popping loose and the mig will be more useful down the road for other things. If cost of a welder is an issue, then it would be better to pay someone to weld on the panels, I have seen panels that have failed using a cheap spot welder, not a pretty sight.