I recommend going to kbb.com and putting in the specifics of your car model, options, and condition. I’m betting that the private party sale value is going to be a couple thousand, in which case I think it’d be worth it to get it to pass emissions for $150. You should be able to sell your car then on Craigslist for pretty close to the kbb value. If you don’t do the $150 fix, you’ll have a harder time selling it, since people will assume it’ll cost more to get it to pass.