SATA to IDE adapters exist, but they are notoriously flaky. I've tried them several times, and never had a good experience (data becomes corrupted after weeks or even days).
If you really need the space, get a USB enclosure for the drive. Albeit it will be slower than IDE, it will be significantly more stable and usable.
If you can't afford an SSD right now, just get a standard SATA HDD - they're cheap enough.
Or if you can wait a couple/few weeks, SSD pricing is expected to dip some (google: "SSD price war". I expect this to be in full stride by the end of the month)