Hmmm... I've been knitting for years and I think the most I spent at any one time has been about 15 dollars on nice wooden needles, and the thought of knitting socks makes me cry.

You can certainly spend a lot on supplies, but I'm always hesitant to spend much on a new hobby or interest unless I
know I'm going to enjoy it.
I think that for a total beginner a set of straight needles and a ball of yarn is all you need to see if you like it. There are YouTube videos showing how to knit/purl/basic knitting (for visual learners), sites like Knitty, and most libraries have books so you wont be out anything in terms of purchasing patterns.
Of course, the same thing goes for crochet. The basic hook and yarn is pretty cheap, the websites and books are available, and you should be able to figure out if you enjoy the actual process pretty quickly.

(to be totally honest, I have had sooooo many people try to teach me how to crochet and I simply can not do it! I knit, weave, embroider, do cross stitch and tapestry, drop spinning, etc but I can not for the life of me figure out crochet. It drives me crazy that all the fun amiguri seem to be crochet.)
OP- sorry I drifted off your topic there for a moment! I totally forgot until I was in bed last night thinking about crafts, but a few years ago I was really into making books. Actually making the paper and then binding the paper into books. Making paper is easy and very low cost (rip existing paper into small pieces... I used the junk mail that was delivered right to my door for free

... put them in a bowl of water till they're soft, drop them into a blender a bit at a time and blend until you have a thin "soup" of paper pulp and water, then pour the whole mess onto a window screen or wire mesh. Squish out the extra water and let the whole thing dry and tad-AH! Paper. You can add color or flowers or herbs or whatever you want to make it spiffier, and you can use molds to shape the sheets of paper... I used cookie cutters I had already). So anyway, the making paper bit is fun for kiddos too (though a newborn probably wont be interested

), you can make all sorts of things, and then there are websites and books that can teach you how to turn that paper into really interesting art books or plain old book-books.
Book making can require fancy tools, but like anything, the basics are inexpensive and easily found... sharp scissors, a hard object for pressing edges into bent paper, thread, needle.
Also, hand made paper might be a nice gift to send to your deployed partner... it doesn't weigh much, it's fairly flat, you can write on it, or put your handprint on it, or your little one's handprint, or flowers that remind you of your wedding or special moment, etc.