single platter 500Gb drives are about $50. The samsung f3 is one such drive. You need to decide if $50 is worth it to you. 1tb drive would be 2 platter, 2tb would be 4.
or spend 80-100 and upgrade your hdd to 1tb (you need more room right? lol) and move the 750gb to the old pc.
last option is an ssd. but in my opinion, ide based ssd's are way overpriced compared to sata.