I wouldn't go with the Jet, you're just getting a more powerful version of the craftsman, and that platen design looks like it won't hold up to heavy grinding. When it's all said and done, it's a sander, for wood. It probably does a pretty good job of that, but for the money there are a lot better choices.
I'll agree with ecos, a 2x72, particularly the kmg style machines (of whatever brand) are your best bet. A grizzly or coote would be next, with the coote seeming to get better reviews in terms of build strength and quality.
I started out with a 2x42 craftsman, I've made a fair number of knives with it. My particular situation didn't allow a better grinder if I was going to stay within budget and waiting wouldn't change that so I made the choice with eyes wide open. Lesser grinder but also a decent drill press and some other tools, was a functional solution. If at all possible though, wait until your budget will allow a kmg style machine and a decent drill press. Decent meaning able to spin slowly and with a minimum of wobble and runout in the design.
My start was $149 for the craftsman 2x42, $120 for the 12 speed harbor freight drill press and $12 for a HF angle grinder to rough cut bar stock. I already had a good vice and some other tools.
Also, update your profile to include your location, some folks may be in your area. Trying out different machines will give you an idea of what will work best for you. The way I work isn't the same as how the next guy works, which isn't the same as the next.... lol, leads to some great discussions here, and we all pick up another trick or five.