You could also check out the current Parks/Korbanth "Graflex 2.0" kits of the lightsaber, or you can wait for Roman's Empire to do his run of replica Graflex flashes. The Parks versions aren't 100% screen accurate though because they're more optimized for electronics and customization.
It's pretty easy to add electronics to any GRAFLEX, replica or not. They're just hollow tubes more or less. Roman of Roman's Empire is the head cheese of romanprops.com. He makes some of the the banginest Obi-Wan replica parts around, and has a run in the works for the GRAFLEX. I'm sure they will be incredilbe and I believe he's aiming for a sub-$200 price tag... which a real flash will probably never drop back down to.
It's pricey, but consider that if you try to go the original parts route $500 will barely even get you the grenade... and then you have the booster and balance pipe... it's enough to drive a person mad.
You can look around here for other threads where people have installed sound / fx. There is also Imperial Royal Arms, which is another forum more focused on saber-building.