What kind of welder should I get?

You can weld stainless steel with any method for regular steel, but the weld and contaminated metal near it WILL rust. If you want to weld stainless, without rust you will have to TIG weld it. Flux core welding is so easy that any idiot can do it without training. They mostly use that where my son works as a fitter. The wire is extremely expensive as compared to MIG wire. HF sells some really cheap a&& flux core welders that might be able to weld some stuff together with a lot of practice (hopefully before the welder goes t%^& up).Stick welding is the old standard. You could get a GOOD Lincoln or maybe Miller used 250A AC/DC welder for a couple of hundred bucks. You would have to install a 220V 50 amp receptacle. You can practice with stick welding, although it is not very good for thin things like a bike frame. If you get a DC stick welder, later you can get a Tig torch rig for less than $200 and rent a argon bottle and scratch TIG weld everything except aluminum. I learned to stick weld first then mig. I have never stooped to flux core, even though my Lincoln 180 mig would do it. My son went to a 1 year welding program after 5 semester of college and is an expert welder and even better fitter. He has showed me a little about TIG, but I have not done much of it.

Great spirit! Before you buy welding equipment start looking for welding classes to learn the process. Go to shops that sell welding supplies and ask about classes and learning opportunities. Many communities sponsor and advertise classes in that kind of thing. Also community colleges offer classes and sometimes certificate programs in that sort of thing that are not attached their academic program. Look on-line and make some calls but that probably a better way to begin than buying equipment.

Inquire at the local Community Colleges about classes in welding. This is a good skill to have and the training will teach you more faster than you can DIY. Also the information about the different types of welding machines and how to use each on different metals. In most major population centers there are probably several such training facilities. As to inexpensive machines you might DAGS for welding machines and try to decide what you consider to be inexpensive. Stick welding and wire feed and TIG or MIG are the more common types. Small portable machines can be less than $500 but IDK what quality they are. For small hobby projects that should be sufficient.