I guess it depends on how much you refine. Let's look at the math.
Refining 1000 of something cost 15 pec with adj refiner. Example 2000 crude oil to 1000 Oil cost 15 pec
For other refiners the price is this:
B1 = 22 pec. Cost TT+25
T-105 = 21 pec. Cost TT+200-350
Adj = 15 pec. Cost TT+2000-3500
Mod = 13 pec
Let's see how much you save with the different refiners. Say you refine 3000 of something/day. That would be 6000 crude oil to 3000 Oil (or similar).
B1 = 3000*0,022 = 66 pec/day *365 = 240,9 ped/year - Baseline
T-105 = 3000*0,021 = 63 pec/day *365 = 229,95/ year - Savings 10,95 ped/year
Adj refine = 3000*0,015 = 45 pec/day *365 = 164,25/year - Savings 76,65/year
Mod = 3000*0,013 = 39 pec/day *365 = 142,35/year - Savings 98,55/year
If you refine 10 times as much the savings will be 10 times as well.
If you pay 3500 ped for a adj refiner (last sale) you might lose ped. If you refine 3000/day for 3 years your savings will be 76,65*3=229,95 ped. If you can sell the refiner for the same price you will have saved some ped, if the price go down 300 ped you have lost 70 ped. If you refine 30k/day your savings is 766,5*3= 2299,8 ped you can sell the refiner at 1200 ped to break even.
If my math is off or if there is something I missed/don't understand please let me know