changing the searching method to "and" and then "OR"

My web page [login to view URL] is an B2B type site where the users could post their ads free or by paying some [login to view URL] paid ads will be shown first comparing by the free ads. searching methode of the web page is in "and" base and then the results are being sorted from the "paid ads" first, free ads and then "date" sorting. I am interested to changing the searching method to "and" and then "OR" methode the same as the Google search engine and then sorting the results in paid ads,free ads and date sorting base. For example if an user input " free online map", software chose the ads having the whole words of the "free"+"online"+"map" and if could not find it, then it finds the ads having two words of the searched input(i.e., for example" free online" ) and if it could not found the same ads then it finds the ads having only one inputted word(i.e., like "free") , however the results should be sorted by the paid ads ,date of the ads and then free ads and date of the ads. If you could amend our searching type to the requested one, please let me know the cost. Please PM me if you have any questions.