Pick up in the World, drop off in SAV and summer rates?

[erikawolf2004]

We are staying in DW for a week and then heading up to Hilton Head for another week and summer rates are coming in around $300 for a week...how far in advance do you book your car rental? Is $300 for a week high...it seems like it to me? Can you add a coupon code to your reservation after the fact or do you have to rebook? Is it alot more to drop off the car at a different location?
TIA

Erika

 

[erikawolf2004]

bumping in hopes someone will have some input.
TIA
Erika