Welding is skill based, if you have alot of skill and ambition you can make alot of money...if you are a poor welder and only want to work in a mechanics shop than you wont go very far.
If you are a skilled welder with lots of tickets and certifications you can make alot of money, good welders usually make $25-$35 per hour and if you are a pipe welder and get on at the right company you can expect $50/hr. A guy that graduated from my college a few years before me has his own welding truck and takes contracts on pipe lines and makes $80-$150 per hour depending on where he is. The sky is the limit, your skill and ambition is what will limit you.
On the flip side, if you are a bad welder and dont want to get certified in anything, $10-$15 per hour is about all your going to see.
There are lots of choices for expanding your career after your a welder, you can go into underwater welding(known as commercial diving), weld inspection, engineering, pipe welding, food grade stainless TIG or if you really want to make some money and have an exceptional feel for the trade you might even beable to get into micro-TIG(basically you lay beads of weld on the edge of a razor blade, aero-space/nuclear plant type of work...not a lot of people can do it but I imagine the guys who can do it are making a ton of money)
Welding takes alot of arc time to get good at, you probably won't start off making x-ray quality welds(I didn't) but after alot of practice you learn how stuff works.
The best advice is to go somewhere and try welding, get a feel for it and decide if it is something you like, I love my job and I have no doubt 100,000/year is not too far off in the future for me. If you hate welding you probably shouldnt do it, you need to be dedicated to constant self-improvement and perfection of your craft. Being a good welder is more than being just another tradesmen, your an artist( kind of a badass artist who makes metal his ***** everyday)
Oh, and you can make alot more money if your willing to relocate and move around to find work, there isn't always a perfect welding job just down the street, sometimes to will have to chase it down in another city or maybe even move to another country for it. The less roots you have in one place holding you there the better, Im like a mercenary, I work for the highest bidder and im always looking.