You can use a default auction php script and modify it... http://www.scripts.com/php-scripts/auction-software/
Specific for domains, check out RadScript. The domain name auction script is in my opinion a bit costly at $335 with their branding and $435 without. If you want a domain portfolio script and want to extend it, take a look at domain portfolio script from both domainforums.com and domainportfolio.us.