Here is a tip on how to cut your EFP transaction costs in half.
Do not rollover your EFPs. Allow each to expire and to be exercised, and then, establish an entirely new EFP to replace it.
If I correctly interpret IB's examples on its website, then IB charges no commission for an expiring EFP resulting in an exercise. The exercise is included in the 50 cent commission required to enter the EFP position. I'll probably have a good test for this by allowing some EFPs to expire this month, unless, for some reason, I decide I need to use the equity for something else.
If I am correct, the cost of an EFP rollover would be $1 per contract (50 cents to exit the old contract, plus 50 cents to enter the new contract). The cost of an exercise followed by an entirely new EFP would be the more advantageous figure of 50 cents per contract (zero to expire, plus 50 cents to enter the new contract).
Bid-ask spread costs would also be cut in half. If you rollover your EFP, you pay the half-spread twice for each rollover, resulting in total spread costs equal to the bid-ask spread. If you instead allow expiration of the EFP, and then enter an entirely new EFP, you only pay the half-spread once, thus cutting your spread costs in half.
So I think this is how to cut in half your EFP transaction costs (commissions plus spread costs).
An exception to this might arise when you find a particularly good bargain on an EFP, one which you do not expect to continue into the future. If the bargain is so good that it justifies paying double transaction costs, then in this special situation, you might want to rollover into this momentarily good deal, locking in this special price, instead of waiting for expiration when you expect that this special price will no longer be available.