A singer 319 has endless possibilities for decorative stitches if you can find a set of 30 flat cams. I like a singer 403 with a full set of cams rather than a 401 which doesn't make any more variety of stitches any way. I also agree a Japanese with a nice set of cams is a good choice. Some are set up to change stitch patterns if you change the needle position. The real old Kenmore machines are my other favorites.
Elna made some great machines and you can find a wide variety of disks for a price. The old green Elna machines have issues with the pulley unless you change it out to one that accepts o rings. The SU is a great machine. I wore mine out.
There are some old Montgomery Ward machines that are pretty cool I had one that closely resembled a Bernina. Keep an open mind about non singer machines.