Anything that bolts to the spring pack (Ez Inch, Zero Rate), will be about the cheapest. Have to figure the cost of new u-bolts in too. Depending on where you get them could be another $20-$50.
Longer shackles only give half the amount of lift. 2" longer shackle=1" of lift. Plus they do bad things for you driveshaft angle. Also affects caster.