Dark City Vapor
has the cheapest ejuice in the land. It's pretty good too and you can get it any way you want it, mix wise. At $2.50/5ml it's a good deal and you should be able to explore what you like that way for cheap. Also, just so you know, should you order a 5 pack of cartomizers from DCV he will throw in a free 5ml of juice which is a great deal. It also has realistic reviews, some of which I wrote myself.
HOWEVER, should you learn how to DIY your juice like I do it will cost you far far less than even that. YouTube is a great place to start learning how to "DIY ejuice". Just do a search, watch, learn. It's easy. Wizardlabs.us has the cheapest nicotine solution in the land in case you care.