I recommend a Japanese made Kenmore ZZ, or a Singer 237. If you find a Kenmore, make sure it is a low shank middle homing machine. These use common 15 bobbins and modern feet and needles. There are an almost endless number of feet available This will serve your needs for many years. A Singer 66 or 15, or a clone will also serve you well, but only straight stitches. All of the above can often be found for $20-$50
I would stay away from Featherweights (too expensive) and 301s (uses slant shank feet).