How many gold coins do I need to unlock all powers on all skylanders

According to this page, which also lists all of the upgrades for a number of the Skylanders, you will need 11,360 coins if you have the 20% discount you get for collecting all ten Winged Sapphires, otherwise you will need 14,200 coins to fully upgrade each Skylander you have.

Since there are 32 Skylanders, you will need 363,520 coins total with the discount, and 454,400 if you do not have the 20% discount.

The linked page also mentions the following note:

Note that you can't buy an upgrade that enhances another ability if you haven't already bought that ability to enhance. For example you cannot buy Spyro's Soul Gem ability "Spyro's Earth Pound" before you have purchased the "Spyro's Flight" power even though it appears on the upgrade screen.