As a fellow small publisher working to get his first product to print, and as someone who has been bouncing around a while as a freelancer, I'd like to offer you some advice.
1) Pay people. Credit isn't enough to the artists who take themselves seriously and want a real go at the industry. At the very least negotiate down to some low prices, but give them some money. Remember, payment is required to be a professional. Here's a good suggestion: ask the artists to take Paypal. By using Paypal you can put the expense against a credit card rather than paying at that moment. I you'd even be better off offering a small amount of royalties or the like -- not ideal for an untested product and company, but at least it is SOMETHING.
2) Always give comp copies. If they put the work in then you owe it to them, yes, OWE it to them, to allow the artists and writers to see their work without them having to pay for it. A reduced price isn't good enough -- sure, it's a nice thing to offer reduced prices for product beyond the comp copy, but not offering the latter at all is just being cheap. There's no euphamistic way to say it. It's just cheap. Spend the money you, as a customer in this industry, would have spent on other companies' products for the next few months, set it aside, and spend it on those comp copies if you have to.
3) Don't try and sell gruel and pass it off as cake. What I mean by this is telling people that having them work for you for free and giving them credit is an "innovative" way to compensate them is insulting. If you'll notice, many game products have a section similar to "about the author" which the author usually writes, allowing them to pimp other products they've worked on, even if for other companies. Just look at a MnM book and you'll see that the last few pages have this for all writers, artists, etc. And to they got money on top of that. Telling people they "don't understand" your innovative compensation plan doesn't help because you're essentially telling them they're stupid for desiring money for their work.
What makes this worse is that you believe that exposure in your book is a desirable thing -- something worth trading money. Now, don't take it as an insult, but look at the facts. You've yet to put anything out. Nobody knows you from Adam. The artists and writers have no idea if your book will tank or be Sliced Bread Re Deux. Every publisher likes to think that they're bringing the "best thing ever" to the market, but it most likely isn't true. Because of this, the people involved have no idea how much exposure they'll be getting from your product, so there's not much value in it to them.
Now, some people will tell you to stay away from using credit cards and Paypal for this sort of thing because it's risky, but if you thought you were going to get into business without taking a risk you were kidding yourself. Most small businesses fail. If you're not willing to take a risk on your business, how can you expect the artists and writers to take a risk on you and the value of getting a credit in your book? Your unwillingness to offer ANY pay, even a negotiated small rate, communicates a lack of confidence in your product on your part because you're not willing to put your neck out on the chopping block along with the people you've asked to help your product.
So, if you're not taking your business and projects seriously -- seriously enough to come to the table with funding or with the understanding that you're willing to take a risk -- quite frankly, why are you surprised when nobody else here is taking you seriously?