Updating My Want List

Hello,

So, I have a question about updating my want list. First let me tell you how I get my "highest price willing to pay number." I take the price of a given coin from Numismedia, coin values, and the average E-bay closed auction price. When finding the E-bay average I specifically look at the closed auction info and ask myself. "Would I bid on this coin?" If the answer is yes I use that for the low or high. For example let's say Numismedia lists this coin for $25, Coin Values lists it for $35 and the E-bay low is $20 and the E-bay high is $45 making the E-bay average $32.50. I take the average of $25, $35, and $32.50 which is $30.83 and I usually round to the nearest quarter $31 is the absolute highest I'm wiling to pay for that coin.

This strategy works well and has yet to fail me but my question is how often do I update my want list? Does the market change enough to where I need to update daily, weekly, monthly? Any idea?

Thanks,
Rich