If it truly is your 'baby' and worth some time. Find (google or better yet the phone book) the name of local welders, pick one that you like for whatever reason. Call him up and tell him you've got a bicycle or a pedal bike not a bike (he'll assume that you're talking about a motorcycle - a more common customer) that has a broken steel thin wall tube that you'd like to repair and can you get his opinion on how best to repair. Then you bring him the frame and you can make an realistic and informed decision. Without seeing the break I'd couldn't give an worthwhile opinion on feasibility or cost.