I know where Andy is coming from, and I don't fully disagree. If you are not sure about framebuilding, spending thousands on a fixture is a bad idea. But I think a fixture is a great thing to have, just removes one more worry. You still have to learn how to use it without introducing distortion. I have used a machine tool table for fixturing. It was very stressful and took a lot of time. A hobbyist might decide they have a lot of time though. If you are building to sell, a fancy fixture on your flickr account has a certain amount of marketing appeal. I used to post that I built a bike in a vise. I did, but years later, I realized it had problems that would have gone away had I used some fixturing. So I don't recommend it. I fixed the problems and I still ride that bike though.

Pick up a used one if you can. Seems like there are a lot of used Anvils. I think you will probably be able to get most of your money out of it. I feel like some of the lesser fixtures will be frustrating to use. They can be upgraded though.

I have used my milling machine table for alignment. Fixturing is easy, and it's a pretty decent reference surface. Then I managed to get a granite plate, problem with that is it's a boat anchor. If you are what you own, a good part of me is a big, heavy rock. Which might explain why I can't lose weight. And as heavy as it is, it isn't quite big enough for a single-setup measurement of alignment. The Bringheli style c-channel alignment system is pretty good.