When I replaced mine on my 210, I first measured the existing rail on the boat. I took my time and was careful, especially around the bow pulpit section. Once I had that measurement, the rest is straight forward. Rub rail comes in defined lengths so I purchased the amount that would meet my measurement and have some left over. I can't recall the exact overage but 4-6 foot sounds right in my case. It may have been less. It goes without saying, more is better in this case.
As to price, you need to know what style you are going to use and then search the net. Type of insert and rail material will determine the cost.
Good luck.
