They take about 3ml x 2 of blood from memory, but i would need to check. (Certainly not enough to affect your performance

)
Cost, it varies hugely, the $300 for urine and $500 for blood is based on a few people seeing an article that had a printout from the LA lab, but having contacted the labs and usada direct, charges vary depending on customer and what agreement is in place.
heres the charges from Australian Anti Doping as a guide
http://www.asada.gov.au/about/fees.html
you will need to convert back into US dollars but as a base you are looking at:
around $1000 for full screen urine with basic blood profile
but then add on additional costs for Epo, Cera, Hgh, Insulin, chuck on another grand for Carbon isotope ratio test
Then add on the tester and chaperone hourly rate, plus travel and accomadation
And yes, the tester (collecter) and Chaperone are employed by a third party WADA approved collection agency and they are responsible for collecting the samples and then transporting them personally to the relevant lab.
Basically:
Testing body be it NSAC, UFC, Vada etc contact Lab
Either they or the lab contact the collection agency
Collecting agents x 2 fly out to the targets location, collect samples
Collecting agents then travel to the lab
Lab Analyses the samples and feeds results back to testing body
Youre looking at Lab costs which vary dependant on what you are testing for, plus travel, accomadation and hourly rate for the collectors
the testing body are only involved at the very beginning and the very end of the process, and during the process samples are just numbered, so the lab never know whos samples being analysed etc.