Why does it need a driveshaft? Unless there is damage to one of the two main pieces, you are probably better off refreshing the one that you have (there's no guarantee that the u-joints, center support bearing and associated rubber and hardware are any better than what you have).

Depending on your mechanic, it might be cheaper to take the assembly to a shop that specializes in driveline stuff, getting it refreshed an rebalanced and then bringing it back to your mechanic to install it.

Good luck!