A Belt of Physical Might +4 (Str, Dex) costs 40,000 GP and actually gives you more than the cited augmentation. Maybe double that figure to 80,000 GP to account for the fact that it does not use up a magic item slot?
David,
I think you meant a Str/Con belt, not Str/Dex.
You are undervaluing his augment considerably, unless the augment is specifically an enhancement bonus and is subject to stacking limitations.
As I suspect the augment is intended, i.e. Free from stacking, 160,000g is more than fair.
A Wish only for a +4 inherent strength bonus would cost 100,000 GP. A Manual of Gainful Exercise +4 (same effect) costs 110,000 GP. If this is an untyped bonus (and would stack with all of your other bonuses), it may well be worth more than that, as Daw said.
And that doesn't count the +2 hp per HD.
160,000 GP sounds very reasonable to me.
Given that the bonus has no type and cannot be removed i'd do, 5,000 x the bonus squared for an untyped bonus
Strength: 16 x 5,000 = 80,000 gp , +50% for being slot-less, 120,000 gp
As for hit points you're not actually gaining con (so no save bonus / death threshold) i'd halve the base number to 2,500 gp x bonus squared
Hit Points: 16 x 2,500 = 40,000, +50% for being slot-less, 60,000 gp
For a total of 180,000 Gp
So yes 160,000 is very reasonable
Making the bonuses untyped is what is driving up the price. You should be able to give this character +4 enhancement bonuses to Str and Con for much less.
As other people have said, making the bonuses untyped is what's driving the price up.
A slottless +4 enhancement to strength is 32000, +2/lvl to hp is probably half of the bonus to con, so about 16000. That's 48,000... for enhancement bonuses.
If you consider +4 inherent bonuses to abilities run about 110,000, an inherent bonus to Str and hp should run about 165,000.