When I built this rig, I bought everything all at once so it was a sizable
outlay. At the time (almost 2 years ago) SSDs were selling for a premium. Maybe when they come down a bit more, I'll upgrade D to a 1 TB SSD.
Maybe it had already been mentioned above, or maybe I even mentioned it. If you use a motherboard with an Intel processor and chipset Z68 or later, you could spend ~$80 on a 60GB SSD, throw in (even an SATA-II) 1TB or 500GB HDD, and do the ISRT "SSD-caching/HDD-acceleration" thing.
If so, I WOULD suggest that you update the system BIOS and get the IRST version update before proceeding.
Later, when you find yourself flush with enough cash to buy a bigger SSD, the 60GB SSD will still have many uses.
Another way to do this on an older motherboard but more recent PCI-E bus version: find an add-in Marvell controller (i.e., Startech PEXSAT34RH) and use the "HyperDuo" Marvell technology alternative to Intel ISRT.
I cannot vouch for how satisfactory HyperDuo might be, or its reliability, but you might look into it. You're still going to spend between $45 and $80 on the PCI-E controller, another $80+ on the 60GB SSD, and between $50 and $80 on an inexpensive but reliable HDD.
Either way -- this sort of thing doesn't require an SATA-III HDD. You'll get the same results from an SATA-II -- for instance, a 1TB Samsung F3 drive if you can find one.