I checked on an oil pressure sending unit for a 69 chevelle SS guages and it was over 100 dollars from GM.

Anyone know of where I could get one cheaper?

That doesn't sound right. I bought one from a GM dealer a few years ago, and I think it was about $15. According to a Year One catalog I have laying around, they sell it for $37 and they get it from GM, so no way it's $100. Try another dealer.