3 is stretching it don't ya think? We're talking about a CPU upgrade, not a whole system. Unless you're pissing money away on stuff like Gulftown you shouldn't be anywhere near $1000 for even a platform change (CPU, mobo, & RAM) to get a worthwhile increase in speed. Or maybe the $1000 just hypothetical?
Well one day I started off with a $2500 system as my first computer. It had Radeon 8500, XP1600+, 256mb of ram, etc. I kept that until it was worth about nothing (besides the monitor and speakers). I realized this is a financial mismanagement on my part. So I decided I'll buy a "base system" consisting of a case/PSU/monitor/speakers and sound card and keep upgrading the main components in it. With this new strategy I have spent a fraction on PC ownership in the last 5 years.
I'll give you an example. I bought my HD4890 for $200 in August of 2009. I sold it this June 2010 for $165 and bought a GTX470 for $202. So my upgrade cost for the videocard was only $37. Before that I sold my Q6600 @ 3.4ghz, Tuniq Tower, 6GBs of Ram, mobo for $295. I bought my i7+mobo+ram for $470. So my platform upgrade cost was about $175. In aggregate then, my last upgrade of the CPU+Mobo+Ram+GPU cost me about $212 (which is around my $200 budget/year).
Before that, I had to spend $185 to go from E6400 @ 3.4ghz + GeForce 8800GTS to Q6600 + 4890. So again that upgrade was around $200 of my annual budget on the PC.
However, my strategy meant 1 key sacrifice - I don't buy the best videocards on release. I wait at least 6-9 months from release to upgrade to give time for prices to drop. This means sometimes patiently waiting for last generation high-end cards when you find a deal such as
$215 HD5870. My strategy would not work if you buy the latest graphics card on release such as a $499 GTX580 and wait 1 year to resell it because you'll probably lose $200 on that card.