I do it myself. Get treated 2X4s and cut to length, cover with marine grade carpet and staple on w/ stainless staples if possible. Take out 1 old lag screw and get the required size and number of new lag screws needed. Do all this before you go to the lake. Load all that up and go to the lake. Launch the boat, beach it, or tie it off and then go to the parking area with the trailer and remove all the old lag screws from the old bunks with a battery operated screw gun, or better yet an impact wrench. First time I used a 9V Makita screw gun. Second time I did it I used a 20V impact wrench. Then mount the new bunks. It does not take that long to do if you do as much prep as possible before you go. If you have a buddy along it'll go even faster. Will most likely save you some $ as well.
I did this as well. got the wood from Home depot, the marine grade carpet from West Marine. Cut the wood to the measurements needed, treated the wood, got the new screws, went to the lake, beached the boat and replaced the boards in about 20 minutes. Then went and fished.