06 Aveo ls, new problems

I knew this might happen, because the last guy who worked on my car had said he needed to use his welding torch to expand a hole to allow a bolt to go in easier. This was, according to him, easier than actually removing the part. Don't ask me why; at the time, I had no extra money to do anything otherwise. Anyway, had a guy attempt to replace the control arms today and lo and behold, he can't on the passenger side because the control arm bolt is welded to the part of the subframe that sits across the front axle(?). The guy said he now needs to see if he can find one at a junkyard, since i'd have to pay a TON by getting it through the dealer. At this point, I don't even know the cost of the part and I have an enormous headache because every time one thing goes wrong, another things crops up.

I had a local tire shop look at the car just prior to this guy and they were the ones who said it needed a control arm. They didn't however, mention the weld and I wonder, is this because they didn't see it or because it doesn't affect their work/ability to fix the arm? They were gonna charge $500 for one side, which is why I went with this private mechanic. I just can't afford to be screwed again and i'd love it if someone can give me some insight.

ETA: The mechanic doesn't know the name of that subframe part, which he said is attached to several other front end components (control arms being one). Anyone know the actual name?