I found 2 (Singer 201 and 347) at GoodWill that were in great condition and both cost less than $30 together. I've seen several at yardsales also cheap. Mine are all straight stitch, but they do everything I want. My 201 is from the forties and weighs in at over 30 pounds and will sew double layer straps without a hiccup. I know this doesn't answer all your questions, but I have enjoyed my older and cheap all metal machines over the newer plastic ones.
My 201 has sewn everything from tarps (silnylon) to double layer hammocks and underquilts. My sister wants to sew her clothes on it, but I won't let her use it.
I've told her it's for outdoor gear only.
I bet RamblinRev will join in and answer more completely than I have on what brands to look for.