I gave the "Clevor"(cleveland heads on a windsor) as an option for a low priced way out. Stock 2bbls can be had for around $150, closed chamber 4bbls for around $300, OC 4bbls for $200-250. With a little bit of work, they'll move a lot of air, up there with the aftermarket heads. Well ported 2bbls have supported upwards of 550hp, and 4bbls much more. But I would also rather have aftermarket heads than stock... but I'd put aftermarket cleveland heads on it. I'm a bit of a cleveland fanatic.
www.airflowdynamics.com.au/cleve2V.html
290cfm int/217cfm exh. A bit more expensive than your normal windsor heads, but they've got the flow to back it up... Theres another great company making heads for clevelands, CHI, but their website is down.