As Lowengard mentioned, you might not fully understand your clients' needs at first, but I disagree to an extent. You have to know what you're aiming at or you wouldn't be at the point you are now. You don't and won't know all of the needs your clients may have at the onset, but you have a pretty good guess. Otherwise, the venture isn't going to be successful.

VG said it well, the majority of the programmers can't design sites or interfaces. Well, they can, but not well. An experience UI designer will be able to approach a project keeping in mind how a client will use it. A programmer approaches it by how it will work and function on the back-end. I firmly believe they should work hand-in-hand or you're going to end up with something that only a more technically savvy person will know how to use.

To be honest, I think you should launch the absolute best product you can keeping in mind your financial limitations. You don't want to start off by launching something that appears to be half-hearted. While the back-end is not, the front-end and element your clients will actually see and use, might appear that way.

Hope that helps anyway. Good luck!