I don't use GSA so much any more, but when I did I set up CS to take captchas first. I was only looking for captcha solves on sites with a PR of 2+ and OBL of 100 or less.
So that meant 90% of the sites GSA found were not suitable in the first place, then CS solved 50-60% of those that were high enough quality leaving a service to do the rest. I found this let though about $10 a day running 60 projects at a time,
I dropped GSA from most of my work and went back to Xrumer.
Xrumer is quite a bit better and runs maybe 10x faster. 100,000 links a day "verified" (of which 50,000 seem to exist - 50% after a random check - but then GSA reports a fuck of a lot of false positives in its "Verified" list as well)
Xrumer solves a lot of the captchas for you - but given the quantity it's still $40 - $50 a day to run at full speed.