Depends on your goals.
If you want a traditional commercial publishing credit, then a co-op is not the way to go. It is considered a form of vanity publishing.
Lots of co-ops are a fronts for self publishing and/or scams. Hard to tell about this particular publisher since you did not list them.
Ask this, what is the publisher going to do for the money you pay up front?
Editing? If so, who are their editors and what professional experience do they have?
Cover design and artwork? Original artwork or stock images?
Do they stock your book in bookstores, as in on the shelves and not just list them for the bookstore to order?
What kind of publishing do they offer? E-books, print books, and do they use pod or offset printing?
What is the terms of the contract? How many years and what is the cancel clause like. What do they say about returning your rights?
What royalty do they offer? Since you are paying them to get started I would think 50% would be reasonable, but then, is that off of list or net? Also, 50% of nothing is still nothing, as in what is their verifiable track record for book sales?
If you really want to go this route, save the money and self publish. You can do all the work yourself, or hire others to help you, and you will know where the money went.
Remember Yogi's law; the money flows to the author...