My vote goes to buying an old machine, especially with that budget.
Reason for my vote:
In the 80's I took my Singer in for repair and the guy told me I wore it out, too much plastic. So I remember saying to him, exactly, "You got anything that's metal, and with no computer?" (computerized machines were just coming onto the market and I knew that was more trouble that I wanted, I just wanted to sew!)
I had never heard of a Viking, just knew Singer from my mom's old trusty reliable.
I bought a Viking 630. With a little resarch, I found out that's the machine they sold to schools, back when schools still bought them, so I knew it was tough and could withstand some abuse (which it never saw with me)
About 10 years ago I got the idea of buying used 630's because I thought, they probably don't even make the parts anymore, so that way I'd have some. So I ended up with 4 machines off ebay, for under $100 each. I thought, if my machine breaks, I've got spare parts. Trouble is, they all work, as does my original!