A "Budget Title" refers to both the production quality and cost of a game. In most cases Budget Titles are of a lower quality and thus also cost less. Budget titles are often marketed to a younger generation of gamers whom would not be able to detect such inferior development.
Budget titles are not always bad however and the lower price may just be used to promote a franchise that isn't likely to sell well normally. Games that are lowered in price long after release are not necessarily considered a "Budget Title".