You're not likely to find
The Figure of Beatrice for anything like a reasonable price online (the Internet has been a great blessing to the used book business while it has been something of a mixed blessing to the business of acquiring used books).
Williams is difficult because he's too simple to be easily understandable. He is also something of a visionary who sees more than he can say. But he says the same things again and again in different ways so that getting to know him in one place helps you to understand him in another.
My practical advice is therefore twofold. First,
borrow Beatrice from the library, photocopy it onto good paper and teach youself the craft of bookbinding. Ironically, a text can be well worth spending money, time, and care to elegantly hand bind when it is emphatically not worth spending the market price to buy a cheap trade paperback copy of.
Second, get to know Williams with a guide. C.S. Lewis can be your Virgil through the rich landscape of Williams' mind. Get the Eerdmans edition of Williams
Taliessin Through Logres and the Region of the Summer Stars with the commentary by Lewis. Then, with your head stuffed full of Co-Inherence, Substitution, the Law of Exchange, Byzantium, the City, etc., you can return to
The Figure of Beatrice better equipped.
Incidentally, if you're going to take my excellent first suggestion, you should probably make two photocopies as you're likely to make a few mistakes on your first try at binding. Then you can correct the things you didn't like about the first one (which we can call my copy) when you make your own. If I'm not mistaken, I believe that you have a friend who's experimented with illuminating manuscripts, yes?