I would just look up the material in cheaper formats. As someone who has read all those early Xmen stories, they were boring. It's only worth reading if you have OCD that makes read every issue of a comic series or really want to learn about some of the most enduring Xmen concepts.

You could probably get the paperback Masterworks for a fraction of the omnibus price. Or a fistful of bucks will get you the digital versions on Marvel Unlimited.