Vintage Singers are great, as are some others. For a low budget, I would definitely go with garage sale used. My friend at the LQS buys and tunes up machine to use in her classes. She says they generally run her about $25 - $50.
When I started quilting, I was told (falsely) that I could not get a walking foot for my beloved 20 year old Viking, so my son now has that. I bought a highly advertized $3K machine that was dead in 3 years. The motor froze up in the middle of quilting. DH had to cut the needle to get the quilt out of the machine! I was told $500 plus labor and a 3 month wait for a new motor. I love my current Janome, but it's way over your budget.
Several people I know have gotten very good older machines from Pfaff, Singer and Viking for peanuts at garage sales.