There is really isn't much difference between the two.
Last time I saw a GS250 online it was $750. Why would you wait for the GS300? It's not a better camera, it's pretty much the same camera.
I doubt if the price is going to come down anymore on the GS250. Places will have less and less in stock making it harder for people to find.
On line retailers will temporarily stick it to customers for early PV-GS300's. MSRP is $699.
Once the initial, brief enthusiasm with the 300 is over, is there any reason to buy a PV-GS250 ? It seems like retailers are going to take a BIG hit if they hold any PV-GS250 inventory as the 300 undercuts it by $200. I doubt retailers can discount the PV-GS250 enough to make it a compelling buy. I would buy a 250 at a decent price but it seems like waiting a month for 300 pricing to settle out makes more sense as it will be newer and cheaper.