Cheap plant tags
Buy venetian blinds at a thrift store or yard sale for next to nothing and snip strips for tags as needed.
The plastic fused to the thin metal used to make the slats is already treated to resist sun rot. One side usually has a matte finish that is great for writing on. #2 pencil lasts much longer than ink, which will sun-fade.
Most of the plastic ID tags sold by professional greenhouses tend to get brittle in about 3 to 5 years. Tags made from blinds will last 7-10 years. Pencil marks are also easy to remove with a scouring pad if you want to reuse labels.
Also, use 2 tags and sink one writing side out into the pot under the media so if a tag fades or is removed you still know what it is.
This double tag system is ideal for club plant sales. The customer gets one tag and the cashier gets the other.