It would seem to me that cheap purchasable non-set IO's would be a real draw. Particularly from the free to play set. If you want to make them particularly useful and desirable make them scale from say 10-30 and then 30-50.
I think pricing would be rather cheap something like 20 points an enhancement would do nicely. This would mean that for 5 dollars or so you could get your character comfortably to the SO territory and it would give you about 20 IO's. Which would be a big help at the low levels for the free to play set.
