Many online sites offer decent zoas & palys both on the high and low end such as vividaquariums.com or myreeftoyours.com. I would check your LFS, most will usually have inexpensive options. Growth depends on many conditions such as water quality, light, and flow; although zoas and palys will more or less grow anywhere in the tank. Each type grows at a slightly different rate. My Armor of Gods are very slow growers whereas my Whammin Watermelons and Orange Bam Bams grow like crazy! Cheers!
I ordered the 20 frag pack from yourreef.com. I added a 10 dollar frag to get the free shipping. All in all it wound up being about 7 bucks a frag. All were nice zoas and many of the frags had more than one type of polyp. Its the best deal I found.