Currently, we keep our replicas and linked clones (C drive) on SSD. For some pools, we also keep the persistent disks there and for some pools we just keep the persistent disks on regular SAN storage. VDI on SSD is a different animal than VDI on traditional storage. We found that it's not just the raw number of IOPS that these things can handle, but the fact that latency is something like 0.1 ms (worst case) versus 5-8 ms for normal disk. Latency kills VDI, so when latency is gone, those virtual desktops perform better and respond more quickly than most physical desktops.
As far as cost goes, you're best to contact the vendor since the price we paid may be more (or less) than what you are offered. It is pricey since it is SSD, but when you compare what it would cost on traditional storage to get the same type of IO, it suddenly seems relatively inexpensive. Combine that with the small form factor (2U), takes less than 400W of electricity and doesn't generate much heat; suddenly it doesn't make sense at all to buy 14+ shelves (x 24 drives each) worth of SAS drives to try to get close to the IOPS this thing can generate.
Definitely do your homework and compare some of the top vendors in the SSD market. There has been alot of innovation and new products brought out in the last 12 months, so it would be wise to understand the differences before rushing to buy a specific solution. We learned the hard way.
