This topic came up not too long ago so I will say here what I said there as well.
I think the price of MS on the servers is a non-issue. Firstly, membership is a non-intrusive micro-transaction, this means that not having the MS does not prevent you from playing the game and enjoying it. Therefore the MS is not essential to the game, no one "needs" an MS they only "want" an MS. To me 350k+ is unreasonable for an MS and therefore I would not buy it. However some people do think it is reasonable and so those people do buy them. If I wanted to sell a piece of furniture for $200 and someone was willing to pay $200, why would I ever sell it to anyone for less than that $200. The price of any commodity in a free market is determined by how much someone will pay for said commodity. If some people are willing to pay 500k for an MS medallion then people will sell them for 500k. Anyone who sells it for less than the market value is either generous or stupid. This is also why the so called "fake bidders" are a non-issue; if someone ups the bid and then does not pay that price and no one else will either, the seller has no choice but to either not sell the product or restart the bidding at a lower price. This means that the problem lies not with "fake bidders" but with the people willing to outbid the "fake bidders". If no one will buy the product at a high value then eventually the value will drop to meet demand.
TL;DR - If you don't want to pay what you consider an unreasonable amount for something, don't pay it, and don't complain.
Addendum- It is also important to note that in-game currency is exactly that, a currency. In the case of PRO the value of the in-game currency is weighed against a constant outside currency, which for all intents and purposes is $5 (the price of a MS medallion). Due to the nature of currency the value fluctuates and may inflate or deflate. A month ago $5 was equivalent to 120k, now it is equivalent to 350k+. That is just how currency works (albeit in a very simplified form).