€ 39.90 is cover price, I think in French a similar system as in Germany applies for printed matter like books, papers and mags (there is a hard fixed price that may not be discounted, unless that fixed price is not lifted by the publisher), so you will find it has the same price everywhere in France. As it is the same publisher as the Mermet 109 books, you may order both from the publisher, but tis may not be advantageous if they do not combine shipping (and their RoW shipping is not cheap). You may try Kenny's as they have a vast selection and very attractive shipping (to Europe at least), and I think also have a webshop for the US which may ship from the US.
It's my privilege - I have been seduced to so many books here ( @JohnT and @Graham Boak excel in this), latest recommendation were the two Lightning books by Stewart Scott. Once you have climbed back to your chair after clicking on them, I can say I only paid a fraction for both together delivered of the absolutely sick price called for Vol. 1 on A. The three Cold War Shields also were not cheap, but are simply must haves if you have any interest in the RAF up to 1970.
It's a cold hard fact that we are talking about niche products, and while there is a healthy 2nd hand market for many, most will never get reprinted. Consequently, prices will usually go up once OOP for a certain time. A very good example is the Classic range. I am shocked to see it's something like 7 or 8 years already, but back then e.g. the 190 and 262 titles were in print, and could be bought at various outlets for as little as 30 €. Have a look at your favourite platform what they go for now. Much the same with the most recent ones, e.g. Ju 88 Vol. 3, Ar 234, SM. 79 and Macchis. With some of them you will be fortunate to find them at all. For this reason, I have made it policy to buy any new Classic title when fresh. If I don't need it, it's at least a good investment.