Yeah, the BeastX 'Pro' upgrade cost is a scam as far as I'm concerned. You cant even find out the price until you actually have the unit, plus you have to pay extra just for the USB dongle which every other manufacturer provides free.
Personally what I did with the Microbeast that came with my last Trex Super Combo kit was sold it still in it's box and bought a different FBL. I went for the Spirit Pro (highly recommended) but the Brain2 or ikon2 are great options too. If you want stability and rescue then selling the Microbeast probably works out cheaper, plus out of principal i didn't want to give BeastX money this way.
Mikado are the other company that does the same scam, it seems to be a 'German thing'. Mikado arent quite as bad because at least the upgrade costs are published on their web site, unlike BeastX.