Yes, it's true you cant change the door frame if you are not hacking the floor. It will damage the flooring. The additional cost of $150/door frame is for a reason. We were trying to keep our renovation costs to a minimum so my hub DIY the door frame himself. It took him like 3-4 weekends to complete 3 doors and it was painful. We are the 4th owner, hence there were 3 layers of paint on the door frame to remove. We bought acid to peel off the paint layers and the acid vapour burn our skin and nostrils. After that, sand it down.