Anyone know where I can buy sleeves of balls?

Without paying pro shop prices? The local golf stores around here only sell boxes, and the pro shops want $14 a sleeve! If a box costs $45, shouldn't a sleeve cost $11.25? I'd like to try a few different balls to see if I like them. I currently play the Callaway Tour i(s). I'd like to try the Penta, Pro V1, and Pro V1x. I've searched the internet to no avail.

Online shopping.  On Ebay you can by mass ammounts of recycled balls for cheap.  Alternativly, I use best4balls (uk based) and I get them for a fraction of the price in pro shops.

eBay, I have done just what you are wanting to do.  It is easy to find sleeves of Pro V1's, not so easy to find sleeves of Penta or Bridgestones but if you are patient they do show up.

You might try talking to the pro at the shop.  I worked out a deal with mine when I did the same thing.  I paid 1/4 of the normal dozen price for each sleeve.

I got to lostgolfballs.com

You can buy AAAAA balls which are 99% 1-hit wonders or corporate logo balls that were never hit. You can get a 50 bucket of them for like 20 bucks... can't beat that.

A lot of chain golf stores will sell sleeves... I know that I've seen them at Roger Dunns and Golfsmith

Shouldn't buying 1 egg cost 1/12 the amount of a dozen eggs?  Why do things cost less (in bulk) at Costco?  I also should be able to buy 1 beer for 1/6 the amount of 1 six-pack of beer.  No, because they want you to buy the dozen, they make more money and it costs them the same amount to service you in terms of employee costs.

I'm sure you realize this and are just a bit peeved because you just want to try a few different balls and don't want to pay $14 a sleeve.  So, back to your original question...I'm sure I've seen 2-ball trial packs at Golf Smith, they were usually new balls that just came out, to try and get people to try them.  They were still more (per ball) than buying in a 12 pack, though.  Other than that, I'd try chatting up guys you play with and go in on a few different balls and split them up.