If you just want to straight stitch, go for a featherweight or one of the older singers. I bought one a 185J for $5.00 at a thrift store and replaced the belt, cleaned and oiled and it sews like a dream.
Check Craig's list or there are usually FW's on ebay. I would rather sew on my featherweight than my $7k Bernina. The stitches are wonderful and they never wear out.