Valuations:An earlier post noted that Scott catalog assigns a value of $50 to covers with certain of these labels. That's somewhat optimistic in my opinion for most of these covers, although there are some label types that are scarce. The values for these covers are a function of the following factors:
(a) the stamps present, and the rate paid,
(b) the origin post office (covers mailed from states with only few covers originating (think Idaho and Wyoming) are more desired than those from say New York),
(c) the destination (Germany represents the destination of over 35% of all such registered covers with exchange labels from New York; while Finland represents less than 1%). Covers to destinations in Africa and the Middle East are much less common than to Europe. Your group of Finland destination covers will definitely skew my Census data the next time I summarize it.

(d) and condition, condition, condition.
Covers mailed from a foreign country, then passing through New York where they receive a label, and then to another foreign country, are generally more desirable than those originating from the US (and only represent only about 25% of the total known.)
And of course, it all depends on what the buyer is collecting, and how much competition he has. If you examine
ebay for the listings of these covers, you'll find asking prices and sold prices all over the place.