Well Technically they will eventually be able to be printed out, meaning that you will only pay for the materials. If you mean what price will fully assembled decent quality 3D printers be in 10-15 years? You'd probably be able to get one for no more that what Epson, and HP charge for the typical 2d printers, which is $80 or so. Having said this, you have to realize that in 10-15 years things will have changed dramatically, so it's really hard to say what kind of printers will be available to us in say 2025. Competition is already starting to drive prices down while pushing the big boys to innovate even more. You will always have expensive, top quality printers while the lower quality ones will be priced much lower. Even in 2025 there will likely be 3D printers costing $25k, but also ones costing $80.