There are some advantages to the quality of an older "all mechanical" sewing machine as typically made in the years 1950-1970 or so. These machines were built like tanks and if reasonably well oiled would exhibit little sign of wear. The older sewing machines were the first machine in the household, predating electric grinders, blenders, refrigerators, vacuum cleaners.... and these machines were ESSENTIAL when first introduced because there was no large "ready made" clothing industry, yet (sewing machines made the "ready made" possible).
For most backpacking work, you have not much real need for fancy stitches, but if you are doing a lot of clothing, you may want to go beyond the sewing machine to a Serger that fully finishes clothing stitches for attractiveness (on the inside or "wrong side").
The best straight stitches are made by machines that make only straight stitches as the mechanical contraptions that allow the needle to dart left and right for fancy stitches allow some lateral needle play not found in "straight stitch" machines, and the straight stitches are really straighter. Most of your straight stitches in jeans, for example, are made on industrial machines which only stitch straight stitches and that do it about twice as fast as a home machine.
Most of the old mechanical sewing machines have better construction than a modern machine, and more expensive mechanical machining was used. A really fine old machine could have cost several hundred dollars in the 1950's, and the inflated cost of modern dollars would be well over $1,000 for such a machine if it were made today.
The older machines were made to be repaired. Not quite that true for a modern "bargain" $100 machine. It isn't difficult to pay $50 for a yearly "maintainence" and routine "adjustments" visit to the shop.
Keep your eye out for these older machines and most of the old Singers, Pfaffs, Vikings, Whites, and a number of others were quite good and can be had for not much money today. Many of them mainly need a good cleaning and lubrication to run great and look good.
The advice to get the advice of a sewing machine mechanic is good, but make sure that you let him know your most common sewing will be straight stitch work with a little "bar tack" (fine zig-zag) thrown in. You won't be doing blind stitches to hem pants and skirts, and you won't be doing decorative stitching. You will be sewing several layers for strong ridge lines with lap fell seams. You won't be doing much work with rufflers or button holes.
I am one of the folks who would suggest buying engineering and manufactured quality in a sewing machine over having dozens of useless "pretty stitches".
A good straight stitch is really a pretty stitch, and a mediocre straight stitch will always look a little cheap... even if you take great pride in having made the piece of gear.