Well the total cost of all IPB3 modifications is roughly $235, you could offer a 25% discount for purchasing the entire range, the price of this would be $175.
Offering lifetime updates in your line of work wouldn't be very feasible, what happens when IPB4 is released, a lot of the modifications would likely have to be remade, and lifetime would presumably cover that, you'd then be making nothing from your work. Initial purchase of all the modifications should cover 12 months like any other purchase, after 12 months the renewal price is usually 50% of the purchase amount, which would be $87, which could be reduced to either $50 or $75 for a rounder more attractive amount.
Anyone serious about running a forum and who has $175 to spend on forum modifications should have no trouble waiting 5-7 days for payment verification, trusted & returning customers could be given a lesser delay, since your own risk is less.
Or you could just scrap the idea of an entire range purchase, and do what IPS does offering a percentage based discount on the more you buy the more you save.
Off-topic; glad the videos system has finally reached 2.0 and looking stable, will make a great addition to my site when I get around to purchasing it.