Frankly, growing up, we didn't have snow bibs... we wore the cotton waffle-weave thermals under our jeans (and.. back then, we didn't have girl ones, so I had to wear my big brother's thermals... eewww!!) .... I grew up in Kansas, and we had plenty of cold snowy weather, also. We built snow forts, had snowball fights, went sledding... so we had plenty of cold exposure!
Our boots were the old fashioned "galoshes" ... basically rubber overshoes with clips to fasten them. We wore them over the shoes we had on.
Most of the time the gloves we had were the cheap cotton jersey ones... yes, they got wet and cold... when we got wet and cold, we came in.
What I'm trying to say is that you don't necessarily have to go out and buy a bunch of stuff for just a few days..... layer clothes, and have extras since they will get wet.
Put a post out on Craigslist... you'd be surprised how much winter stuff is for sale there even in Texas.... that will really help with the budget.
Or... you can also ask your FIL and his wife if any of their friends have some snow bibs and boots you could borrow for the stay... be sure to pick up some good gloves, though.