Or you could buy a PC with a Celeron CPU, which was obsolete way before launch.
They overclocked well though, I think you could run the 300Mhz chips at >400Mhz.
I also believe you could get motherboards that supported 2 Celeron chips. I have no idea how effective/useful it was, but it was certainly a cheap/interesting way to get multiple CPU's.
When my dad bought one he told me outright "this is for poor people".