If you're looking for budget stuff then find someone who's pulling them out of their truck and replacing/upgrading or selling their truck. Look in our Forsale section. Evilbay is also a good place to look for someone selling their old stuff.
The "cheap" gauge you by today is going to be very hard to convince yourself to buy replace one that "works" later on. Not to mention that you're not going to save too much especially if you buy new ones. Diesel gauges are not like water, amp, & oil pressure gauges where everyone makes them and there are cheap china junk on the shelf at autozone. The big names in gauges make them and you get the big name quality and the price too.
If you're on a tight budget, visit the vendors for this site and some of the other sites supporting the diesel hobby and compare prices. I know when I bought mine GOS performance had bought a large supply of gauges when a company went under, so I got a great deal on my pillar pod a gauges.
Either way you go patients is the key to saving money.
Don't go cheap. If you can't afford a good pyro then you can't afford to chance a motor malfunction with high hp mods.