Back in 0.12 I really wanted longer underground belts both for ups and because it would enable some nice options. So I made this super simple "mod" primarily for myself, and ended up releasing it on the newly released mod portal. It's changed a bit over time but it is primarily a "balanced" mod to allow some flexibility. All costs are scaled based on the range added. For instance if you set medium range belts to 2 (default) it'll cost 2x as much and have twice the range.

It adds:
Underground belt medium
Underground belt long
Fast underground belt medium
Fast underground belt long
Express underground belt medium
Express underground belt long
Pipe to ground medium
Pipe to ground long