My willingness to spend so much money, and no more. One must learn to spend less than one has in the bank, or has as available credit (both would apply, in my case.)
Wise advice...my 17" Sony Triniton, purchased in 1983, is just now going to pink screens when I turn it on (rarely)...however, it still perks up after a couple of minutes!!
I have a $99 Plextor HDTV setup with my laptop and 19" monitor, and the over-the-air HD is superb!! Everything from Nova to football is very nice!