It really depends... Normally come in pairs...
sometimes drug stores have some funky ones (holloween version) and not very expensive...
And some drug store brands are pretty good and not so expensive (less than $10)
Some Daiso ones are ok ($2)
MAC, Shu Uemura ones are nice, but more expensive la of coz...
I normally stock them up whenever see them on sale/outlets/pretty ones.
It is very important to remove the glue and put them back in the case afterwards if you want to reuse them... Depends on the quality, for me it is also around 4 times...