I love this idea, mainly because I have eliminated my needing to get plastic cups every time we have a gathering. Actually the part I hate most is trying to remember if I need these cups and over buying them. I got these plastic tumblers at the end of the summer for a steal, 4/1.00 and bought 36 of them, that should be enough!
I also got some chalkboard contact paper and cut out with a paper punch some scalloped circles. Adhere to the cups and get out the colored chalk. Guests can write their name or a message to know which glass is theirs. The circles will stay on through a few careful washes.
The only place I was able to find this Contact paper was on Amazon, I think I paid about 6.00 for a 18 foot roll, add shipping and it was around 10-12.00 total for the roll. I tried several hardware stores, family hardware stores, school supply/teacher supply shops and could not find it locally anywhere.