I think a really nice and thoughtful idea would be to get the priest(s) a gift card to a nearby grocery store. A Wal-Mart gift card would be a great idea if you have a Super Wal-Mart around because it would be usable on both food and personal items. I think $20 is more than enough.
Also, when I was ending my spiritual direction, I got the priest who was helping me a nice "thank you" card and a holy card of St. John Vianney, patron of priests. It was during the year of the priest, so I thought it was appropriate especially for that time, but he is a patron at anytime. Don't go too overboard. Priests are not in it for the gifts and money--it is a special calling from God. I'm sure, though, they will appreciate the thoughtfulness of a parishioner. :)