The 1979 Penthouse porn film Caligula starring Hellen Mirren, Malcolm McDowell and Peter O'Toole had a budget of $17.5 million. Caligula is an actual porn film as the sex was real, not simulated. The 2008 porn film Pirates II: Stagnetti's Revenge had a budget of $8 million. It’s not usual for a feature-length porn budget to cross the million dollar mark. Of course most porn films are shorts and don't have anywhere near these budgets or quality of production (two or more people romping in front of a web cam), but that can be said of the general film industry as well. More than 6,000 feature films are made every year, and tens of thousand (if not hundreds of thousand) shorts. Most are crap.
The 1995 porn film Uninhibited ($1.5 million) stands out as it was so good that HBO and the USA Network picked up the film after editing it down to an R version.