I understand budget issues. If you can find a way to get a z77 and the Ivy CPU it would save you $$$ in the long run and you'd be up-to-date with no need to upgrade the board or CPU for a long time.
The SB & IB CPU's are around the same price so, you might as well get the i5 Ivy CPU. The Ivy prices have just dropped a bit too.
Intel cuts desktop Ivy Bridge pricing before it is even launched
http://www.tweaktown.com/news/23564/intel_cuts_desktop_ivy_bridge_pricing_before_it_is_even_launched/index.html
Not sure if that takes affect in your country though. Which country are you in?
So, if I were you, I'd either get a z68 that has the bios update for the Ivy CPU's & get a Sandy Bridge i5 or, go ahead and get a z77 with an Ivy Bridge i5. I don't think there's going to be a big difference in price. Going with the z77 & Ivy CPU would save you from updating for a few years though saving you money in the long run while keeping up to date.