Harbor Freight has reasonable prices for headlight bulbs if they happen to stock the kind you need. I’ve never tried their brand though, so can’t speak to the quality. 9006 and 9006 here on this link for about $7 each. Rock auto list the 9004 – the one I use for the Corolla – at about $2 each.
http://www.harborfreight.com/catalogsearch/result?q=headlight+bulbs