On Ebay, the cheapest selection were ready-made necklaces with a couple dozen agates. I assume these are small to medium sizes. I bought a few for not very much money, and won some bids on necklaces for ridiculously small amounts of money.

I noticed that many larger agates, with more 'natural' agate colors, are sold as Bonsai decorative accents. Guessing no holes in those!