ebay has alot of leather strong sewing machines even check used equip you will be surprized at the demand . Alot of people use them want them more then you would think as you say to yourself uhmm id like to make some seat covers and reupholster some stuff and then you start looking and bam there is a strong demand for this equipment.There are inexpencive machines out there even on ebay just dont expect it to last a life time.As for the machines that have and will last a life time they are sought after like any other item you start to have interest in.Id get a cheap inexpencive ebay brand that advertise its for heavey duty leather work and while you use it keep an eye out for a high quality old school ones they pop up but takes a lot of time scouring used equipment stores.
when I have looked in the past it seems the guys that have been it it for years know the brand names.And it just seemed to me alot of effort to get a good old machine .I even worked for LaBaron and Bonney in Ma (they make model A era Ford interiors and also more recently early Chevy interiors.Their machines they have had forever.
So it seems the good ones are still in use.My conclusion was to get a use a cheap machine till I took the time it would take to trap and good old one.Good Luck in your search.
jb, look for an old treadle style singer thats been converted. the older the better. i used one to stitch heavy gauge vinyl coated fibreglass cloth for years where i worked. the thing would go and go and go. the parts are easy to get, and they are so simple even you could use one. like everything else you own, keep your fingers away from the needle. i saw more then one person put a stitch through their finger using that machine. its one of the things i wish i had still. a really awesome machine.
Ditto on the treddle machine. I sew all my vinyl and leather seats on a 1923 Singer. I even did a rear window replacement for a friend's Miata-worke great. The key is to find the proper needle and thread. I'm guessing one that's been converted to electric would be great. I just keep pedaling.