SSD prices are plummeting. A UK-based computer retailer, eBuyer, is offering OCZ 240GB Vertex Plus SSDs for £89 ($144, €109) - a price which only a few months ago would have bought you an SSD with just half that capacity
Hard drive prices are still keeping pace, though, with multi-terabyte disks seemingly halving in price at least every year.
Remember, for high-performance computing, the type of SSD matters as much, if not more, than the capacity. Software supporting the solid state devices also matters. If you're using an SSD for a specialist purpose, like in an external recorder (from Sound Devices, Atomos, etc) it is vital that you check with the manufacturer that your proposed purchase is on the "compatible" list. If not, it might simply not work, or, worse, it could corrupt your day's shooting. There are many different grades of SSD, and PC industry site Tom's Hardware recently identified no less than ten distinct levels of performance in SSDs.
Use of this type of storage in very high performance shared storage systems growing, but that performance comes as much from the careful setup and supporting software as from the devices themselves, so don't expect commodity pricing from suppliers of specialist systems just yet. If anything, the rapid generational change in SSDs can make supporting them more expensive!
Nevertheless, for most general purpose computers, choosing solid state storage has just transitioned from "expensive" to "obvious".