I've been reading through the customization rules in Campaign Operations as closely as family time has allowed this week, and it struck me: Class A Refit kits are essentially free with regard to time and complexity (a 1x time multiplier, and a 0 penalty to the roll). This means the "reduce MG ammo and add armor" kits are totally worth it!
The time to complete each refit is 120 minutes (to reduce the ammunition bin capacity) plus 5 minutes per armor point added.
The Locust (LCT-1Vr) came up first alphabetically, so:
Reduce MG ammo to 0.5 ton, add: 1 point to the Head, and 2 points to each arm. It's 5,500 if you stick with RAW rounding, but Fractional Accounting would reduce it to 3,438 C-Bills (with 137 rounds of ammo).
Phoenix Hawk (PXH-1r):
Reduce MG ammo to 0.5 ton, add: 2 points to the Head, and 3 points to each arm. That's 5,500. With Fractional Accounting, reduce the ammo to 75 rounds, and max the arm armor (i.e. one more point to each, which means they can survive an AC/20 hit with 1 point of IS remaining). That would cost 6,875.
Stinger (STG-3Rr):
Reduce MG ammo to 0.5 ton, add: 4 points to the Head, and 2 points to each leg (so they can survive a PPC hit with 1 IS remaining). That's 5,500. With Fractional Accounting, reduce the ammo to 50 shots, and add 2 points to the arms (so they can survive Large Laser hits). That would cost 8,250.
Falcon (FLC-4Nr):
Reduce MG ammo to 0.5 ton, add: 2 points to the arms and CT, and 1 to each leg. 5,500 C-Bill cost.
Vulcan (VLC-2Tr):
Reduce MG ammo to 0.5 ton, add: 3 points to the side torsos and 1 to each leg. 5,500 C-Bill cost.
Crusader (CRD-3Rr):
Reduce MG ammo to 0.5 ton, add: 4 points to each leg. 5,500 C-Bill cost. With Fractional Accounting, reduce MG ammo to 75, and add one further point to each leg, cost 6,875 C-Bills.
Thunderbolt (TDR-5Dr):
Reduce MG ammo to 0.5 ton, add: 1 point to each leg and the CT. 5,500 C-Bill cost. With Fractional Accounting, reduce ammo to 162, cost 1,875 C-Bills.
Warhammer (WHM-6Rr):
Reduce MG ammo to 0.5 ton, add: 3 points to each side torso, and 1 point to each leg. 5,500 C-Bill cost. With Fractional Accounting, reduce ammo to 25 shots and add 1 point to each arm, 3 points to the CT, and 1 point to the CT(R), cost 9,625 C-Bills.
Battlemaster (BLR-1Gr):
Reduce MG ammo to 0.5 ton, add: 2 points to each arm and leg. 5,500 C-Bill cost. With Fractional Accounting, reduce ammo to 25 shots and add 1 more point to each arm, and 4 points to the CT, cost 9,625 C-Bills.
The philosophical question becomes: how many refit kits does a Tech have to install to be able to do it with just the parts on hand? ;)