Price drop to fixed ammount with crossed-out old price

Hello
We are a company from Slovenia running a webshop www.naracamicieonline.com
We need an extension to simultaneously change all prices from a defined category to fixed ammount (in our case 19,90 or 29,90 EUR) also we need that the old price must be still visible with different colour and crossed-out.
If anyone know that that kind of extension exsist or is able to do it , please help us.

Thank you in advance

p.s.
Currently we have multi discount module that can lower prices by percentage or fixed ammount but doesnt fit our needs when we moove all new collection to outlet and items from different prices drop to same ammount of 29,90 EUR.