Spices are definitely a favor that will have a spot in every guest's pantry. We also love the idea of letting guests choose sweet or spicy! Buy them in bulk for cheap at international food stores, bargain stores like Walmart, or the dollar store. Store them in jars you get for under $1 from specialtybottle.com.
If you don't feel like making them yourself, you can buy them for a little more money. These mini spice jars, for instance, are $48 for 30.