IMO, the thought to fix is up to who made the machine. If it's a high end machine (which I'm guessing it's not, since you're already having problems with them), yes by all means, fix them. Jem / Martin, Rosco, Omnisistem all make great foggers and yes, they are expensive.
Anything bought at Part City, Spirit, Spencers, etc, IMO if you get a season out of it, great. If it still still works the next year, even better, you should feel lucky. This includes even "expensive" low end brands like Chauvet. We picked up 12 of Chauvet's F-1050's, $110 a pop if memory serves. They were great, when they worked. One or two died the first season, then a half dozen didn't work the next season, even after being properly stored. We didn't get more than 3 seaons on all but a few.
Here's my take in general on Fogger's in the haunt industry;
If you run a year round attraction, by all means, buy theater grade foggers. If you have a haunt that has a layout that allows you to run a few large foggers and duct the fog throughout the haunt, by all means, spend the money and buy a theater grade fogger.
If you don't fall into either of the above categories, IMO you're better off buying new, cheap foggers every year. We have a ton of small rooms and they're all spread out among 4 buildings (we're an indoor / outdoor), so we don't need a huge fogger that can fill a stadium with fog in 30 seconds. We run much lower durations, maybe 10 or 15 seconds every 5 or 10 minutes in each room. We generally end up buying 10 or so new foggers every year and we usually are able to pick them up for $20-30 a piece as a "bulk deal" from the local Spirit and Party City. Running out for an hour, spending $200-300 on new foggers and being done sure beats screwing around with them, troubleshooting them, ordering parts, waiting for parts, installing parts, etc, at least for us.
That's my 2c.
Operations Manager & Technical Director
We're headlining the HauntCon 2012 tour! We hope to see you there!
A big thanks to all of those who came out to visit us on the '09 MHC Pre-Con Tour!