An older all-metal Singer (made in the 60s or earlier) would work for many layers of heavy fabric. The 401, 403, 500, 500 are particularly ideal, or a 201 or 15-91 straight stitcher. You can usually find these on craigslist reasonable and they are fairly easy to service yourself. My other choice would be a Viking 6000 series, which have low gear (has full power at 1/4 speed). With the Viking 6000 series you have to check if it has been serviced and/or had the internal cam replaced as they are prone to crack, and it can get gummy and freeze up. I got a 6020 for $5 because the cam was cracked but after a $200 overhaul it sews like a tank.