There are some great vintage sewing machine groups (Facebook, Ravelry, probably reddit and patternreview), and the older machines are quite reliable and far less fussy than the newer electronic ones. I have a 25 year old Kenmore (made by Janome) which has never needed service, an 80 year old straight stitch Singer, which will outlive me, and a $200 Brother serger (but I sew a lot of knit garments, because that's what I wear).
Perhaps you can sew knits without sergers, but I wouldn't want to. I have so far resisted the call of a coverstitch machine.