A 128 GB SSD suitable for a Windows 7 system drive can cost as little as $110. Besides giving better boot performance, it greatly speeds up disk IO. Also SSD performance isn’t affected by data fragmentation the way a physical hard drive is.
I just picked up a 240GB SSD (Intel) from Newegg for $140 on sale.
She's never had a SSD before, so she's suitably impressed by the speed-up.