Average cost of a postcard in europe?

i'm trying to raise funds for my travels by offering gifts for certain $'s of donations.. one gift would be a postcard: if somebody donates $7 (£4.50 /~€5), i'll send a postcard from europe to them. i'm figuring postage will be up to $2 and the postcard up to $3 (~2 €/£).. does that sound about right? around 2 euro/lb for a postcard?