I would like to hear thoughts and comments on a Dakota action for building a custom gun versus Model 98 Mauser. What would a standard length Dakota action be worth on the used market[.338 win]

You should probably get a general idea by accessing Brownell's site and checking on the price of a new one. I don't think I have ever seen a used Dakota action listed for sale.

There is a very good chance the Dakota would be cheaper in the long run.

I recently choose Dakota for a pair of matched rifles I have having built. I did so for two reasons. The first reason is one action must be left hand. The second is I couldn't find any Mauser left hand actions available and I looked as well as spent two years plus waiting on Hein to produce.

I went with Dakota almost by default but I am sure we will be very happy with the results.