Immediate Dentures: These are usually a temporary means of helping you transition to successful denture wearing. Because of the muscular readjustment required, as well as the natural shrinkage of gums, the dentures which are placed immediately after tooth extraction won't fit as well as permanent dentures made when the healing is complete. They do, however, provide you with new teeth right away, and give you time to adjust.
The reason the cost for either "new" (conventional, non-immediate) or "replacement" full dentures is the same is that for the most part all of the steps that the dentist must take, and the number of appointments needed, are essentially the same in both cases. Also, all of the costs they encounter (like the price they pay a dental laboratory to fabricate the appliance) are the same too.
Before I close, I'd like to add a word on fees as well. I almost hesitate to call this an affordable dental office, simply because they obviously put care first. All dental offices should do what this office does and provide options, but few do. It's that commitment to patient care and letting you choose what's right for you that makes them more affordable, versus the offices that cut corners to save you a buck. That's a major difference worth noting. They also have an on-site lab, which saves costs as well.