There will be another product price on the site, Reserve Price. One is a default price. So the total price will be two: Regular and Reserve. Both prices will be displayed under each product and Add to cart button will also be there for each price. Customer can either click the regular price button or Reserve price button. Now the thing that needs to do is to add the selected price into the cart and that price should take into effect in all the pages like checkout, sales order email and backend, etc. I hope once the selected price goes into the cart, that price displays automatically into all over the site. This could be a simple task but a Magento developer who can creata a module to override the cart controller or model, etc is requested to bid.
But for this, there should be a price attribute on the product page of admin. you can use Special price field but the calculation should happen automatically. The reserve price should be 25% of base price and if you put 100 in base price field, then the special price field should come out to be 25 automatically.
The site url is: http://lajollaartgallery.com/artists and the product page is http://lajollaartgallery.com/harbour-night.html. Currently the Reserve price is being displayed by Special Product.
PS. Please don't apply if you can't fix it in more than a day.