I am a driver for UPS (and I happen to live in Seattle, too) so here are a few tips:
-It will be cheapest if you pack it yourself and drop it off at a UPS Store, Office Depot, etc. Don't take it directly to the UPS building itself, as they will make you open the box and inspect it before shipping.
-Try to keep the box less than 1 cubic foot in volume or the price starts to go up.
-A flat box is better than a cube-shaped box, it is less likely to get tumbled around.
-The box will require a shipping document which lists the contents, country of origin, value, etc. If you go to UPS.com to print your shipping label, you can enter all the info at that time and it will print your invoice for you.
-The most important thing for you I think will be to make sure that it is legal to ship your gecko into France, if there is a customs hangup it will be there.
-I did a little research, a 2 pound box from Seattle to Paris, 8x8x8 inches will be about 78 dollars and will take 2 days.
-You need to write "Live Harmless Reptile" and the species name on the outside of the box to comply with Federal Law.
I don't know the exact regulations for FedEx or DHL but I imagine they are similar. The big question is, will your gecko be okay in a box for 2 days? You might want to post on the Shipping Discussion Forum and get some feedback. With heatpacks the temp should be okay, but I wonder about the air supply. Anyway, that's about all I can think of for now. Hope this info is useful.
Chris