i have an eyetv 250 + hooked up to my 17" imac and it works great, DVR capabilities are good and editing of recorded shows is real easy, you can then export them to itunes (currently exporting 'my name is earl', 'the office', 'heroes', and 'it's always sunny in philadelphia', while my daughter is watching spongebob squarepants), but it does depend on what kind of cable you plan on using, i have normal analog cable that doesn't require a box, if you have a digital box than you need an IR blaster to change the channels using the eyetv remote
EDIT- I paid $200 or $250 for mine I do believe, but I think macsales.com has them for $150 or $100 refurbished, but even at $250 I feel it was completely worth it