I have a Miller SideKick and it's great for light-gauge work. It uses the same Miller M-10 gun as a brand new Hobart Handler 187 which means consumables are readily available.
I think it is well worth $100 to repair, especially if it comes with the original gas gauge and gun. Like most 110-volt welders, you can expect to weld up to 12-gauge with one-pass penetration.
The Sidekick can be picked up by one man, but it is somewhat less than portable when compared with modern 110-volt machines. Conversely, it is built like a tank, has a world-class arc and a massive transformer.
The 110-volt model is rated at 90 amps at 18 VDC with a very conservative 20% duty cycle. (Miller did make a much rarer 220-volt Sidekick with a 30% duty cycle.) In real-world use, I don't think I have ever heard of a case of anyone having overheating/duty cycle problems with a Sidekick.
One caveat: Older Sidekick's did not have external jumpers to change polarity between flux core and solid wire gas. It's easy to determine which version you have. If your welder has one, the polarity changeover board is located directly above the gun feeder when you open the welder door. There should be a polarity configuration label next to the board.)
The Sidekick is designed to accept 8-pound and larger wire spools. You can either make or buy an adapter for the smaller 2-pound spools common at places like Tractor Supply, HF, etc.
The Miller SideKick manual can be found here:
Sidekick manual...
You can see one in action here (this is an early model without the polarity changeover board):
Welding with an early model Sidekick.
Here's a relatively recent discussion on the Sidekick from guys who own and use them:
Sidekick discussion.
