They are pricey imo, but if you want to pimp your items out then go for it
$10 = 1k coins
$20= 2k coins
$50= 5k coins
*I did not include the bonus % for each purchase.
However, there are other ways that you can get coin items for free. There are events now on forums hosted by the GM, so take a look on those to see which interest you. Be sure to keep checking back though for more events.