Depending on the currency we're talking about, $400 might be a bit ambitious. iFixit has them going for US$550 which is quite steep, but you know you'll be getting a quality, new product.
You might be able to find a cheaper used logic board ion eBay or something, but you won't know whether it's good 'til you've installed it and there won't be any mechanisms in place to get your money back if it doesn't.
My Powerbook needed a new logic board, and I just ended up letting a local Apple Store take care of it. It's going to set me back $350, but it's a flat fee, so if they screw anything else up, or if anything else is also a problem, they'll fix it. You might want to call up a store near you and see what they'll ask for the repair.
well my failure is self induced. I messed up the logic board upgrading the hdd, i didnt tell my local apple store that but they gave me a third party place to call and they told me that it would cost $700 with labor! but i found one on ebay for $350 which is the lowest I have yet to find.