If you have $3.50 per bottle and some crap you want to get rid of, it's time for the Zoya Polish Exchange!
Any bottle of polish (except Zoya Qtica or Nocti) can be sent in, with $3.50 per bottle you want to exchange, and you can pick a bottle of Zoya polish to be sent to you in return. It's not cheap per se, but it's a lot cheaper than their regular prices!! You must send in at least six bottles. It lasts until June 30, so you have a bit of time.