I can make you custom labels for your cups. They are %100 compostable because we use a medium gloss paper rather then the plastic coatings. Right now I can do several different shapes like round, oval and square of different sizes and we dont have any min order or set up fees as long as you have the basic design already done. I can tweak it a bit to fit but there is no charge for that.
Stickers can be as little as a few cents a piece and a much nicer option then a stamp. Let me know if you are interested via email. Jarred@chefstack.com
I would have to second contacting Espresso Parts NW. They will custom design a rubber stamper just for you - if you concieve it, they'll create it - and the stamps transfer great to paper cups. This is definately a cost effective way of personally branding your own cups with your logo, as well as giving your product a grass-roots look that many people appreciate. The additional labor of actually stamping your cups is a breeze, taking about two minutes to do a sleeve of cups, and the ink won't smear as you restack your finished product. I'm not sure I'd consider any other option, personally. Also, the folks over at Espresso Parts are seriously the best at what they do.
You may want to check out woodruffandco.com.au. Following them on instagram and they seem to do a heap of coffee cup stamps.