Only 2 are recommended most of the time (Kweld or Malectrics) but if you say affordable because you want to save money then you’re barking up the wrong tree. Compare them 2 depends on what you want kweld seems to be better quality and gives more consistent results but others will argue thay prefer Malectrics. People who build mutiple battrys seem to go for kweld or larger more industrial machines. But it cheeper to buy a battry unless you building 1/2 a dozen or more.