davemac :
I would definitely consider $120 to be affordable. I'd like to build a complete system for around $500 - $600 and maybe keep my existing case/powersupply if possible...Also starting to wonder if AMD is the right choice or if I should be checking out some Intel boards.
AMD is currently offering the better value and future upgrade paths on a moderate budget. Up-coming Socket AM3 processors will be compatible with Socket AM2+ motherboards, at least motherboards that will receive BIOS support for AM3 (not all of them will). Most or all motherboard vendors now are indicating AM2+ motherboards that will be supporting AM3 processors (with future BIOS).
Between $90 ~ $110, there are several full-featured AMD 790X/GX or NVIDIA GF8200/8300 boards to choose from. I've been doing this a long time and I've never been more impressed by how much $100 is buying right now in a motherboard. For that matter, I'm impressed by how much $80 is buying right now.
You can build Intel LGA775 C2D/C2Q system for $500 ~ $600 but Intel is winding down LGA775. LGA775 will have no new product releases outside of mid-range and value segments. Even those are certain to be respins or revised steppings of current 45nm offerings. Core i7 is your only path to future Intel processor releases and it will cost you a lot more than $500 ~ $600.
Just be sure to check manufacturer CPU support lists for TDP limits, if the TDP limit is not conspicuously disclosed. There are three main TDP segmentations for current AM2+ and forth-coming AM3 processors; 95W, 125W, and 140W.
Some boards support up to 95W max or 125W max, but online resellers routinely fail to disclose the TDP limit in their online catalogs (including Newegg), even though the manufacturer website discloses it. e.g. ECS GF8200A Black Series is limited to 95W MAX TDP and ECS website discloses this, but resellers rarely convey this important bit of info.
If the TDP limit is not clearly disclosed, you can make reasonable inference from the CPU support lists provided on manufacturer websites. If there are no 125W models listed, its a safe bet its not supported. Same for 140W TDP models.