For now, this modification is not well balanced. Belt portals are way too cheap. My suggestion is to make some variants of each color; let's say:
Local - 10x Underground belt
Planetary - 100x Underground belt
Stellar - 1,000x Underground belt
Interstellar - 10,000x Underground belt
Galaxy - 100,000x Underground belt
This is only a first draft and should be calibrated carefully.
Each better variant could have a greater range.
