It is easy to calculate. Not for gambling on FOMA or other indoor mining places. Only for single drops, because true miners working for MU and most drops in this case are single, not double or triple.
It is possible to do up to 1200 attempts per day planetside (based on fact that you are not a robot and need some time for excavating your findings). This is approx 4-5 hours of hardcore mining per day.
For level 7 amp:
120 PED (L) and UL Amp, 40 possible attempts. 9% current MU.
Economy for level 7 amp is:
30x10,8 PED=324 PED per Day savings on MU
additional decay of the Portable Repair Unit 30x0,065=1,95 PED.
So you can save 322 PED/day, 9660 PED/Month, 115920 PED/Year
ROI if price = 150k is 16 months
IMO fair ROI is ~1 year, so fair price is ~110-120K
For level 5 amp:
200 PED (L) Amp, 100(Ark), or 99 (other planets) possible attempts. 3% current MU.
113 PED UL Amp, 56 possible attempts.
It is possible to burn up to 12 (L) amps per day planetside, or 21 UL amps
Economy for level 5 amp is:
12x6 PED=72 PED per Day savings on MU
additional decay of the Portable Repair Unit 21x0,065=1,37 PED.
So you can save 70,5 PED/day, 2115 PED/Month, 25380 PED/Year
ROI if price is 100k = 4 years
Fair price for Level 5 UL is 25-30K (ROI 1 year)
Same calculation for old MU 109%:
12х18=216 PED
Savings: 214 PED/day, 6420 PED/month, 77040 PED/year. I know about one sale for 85K in the past, so it was close to fair price. With current MU 103% on (L) version, 85k or 100k or 120k is just ridicolous price
For level 3 amp:
114 PED (L) Amp, 114 possible attempts. 6% current MU.
100 PED UL Amp, 100 possible attempts.
It is possible to burn up to 11 (L) amps per day planetside, or 12 UL amps
Economy for level 3 amp is:
11x6,84 PED=75,24 PED per Day savings on MU
additional decay of the Portable Repair Unit 12x0,065=0,78 PED.
So you can save 74,5 PED/day, 2235 PED/Month, 26820 PED/Year
ROI if price = 28k is a little more than 1 year
Fair price for Level 3 UL is 25-27K (ROI 1 year)
For level 2 amp:
100 PED (L) Amp, 200 possible attempts. 6% current MU.
78 PED UL Amp, 156 possible attempts.
It is possible to burn up to 6 (L) amps per day planetside, or 8 UL amps
Economy for level 2 amp is:
6x6 PED=36 PED per Day savings on MU
additional decay of the Portable Repair Unit 8x0,065=0,52 PED
So you can save 35,5 PED/day, 1065 PED/Month, 12780 PED/Year
ROI if price = 10k is less than a year
Fair price for Level 2 UL is 12-13K (ROI 1 year)
Important!
This calculation is valid only for current MU's!
Added: Prices for gamblers can be arbitrarily large, they have enough money for losses