I have only 1, not listed nowhere. Even I still thinking if I want to sell the key or not and use myself, already have seen offers (who were already purchased from other customers/clients) for DotA 2 Beta Keys (not on Sythe or trademarket forums) that have been sold for such a high price, so prepare a price between $300 and $500. For Diablo III is hard to get similar as DotA 2, but the difference is that DotA will be played from 50-100k on Steam, D3 - from 1-4 millions total worldwide, and therefore the price for beta key is much more - between $400 and $900. For CSGO beta key in the end of Aug offer for $1000 which was sold in few hrs, now they cost around $100-$200.
$72 = €53 (my pre-order price). RRP you know is €60, in most stores in Europe it's €59,99 (except UK - different currency, market, people, stock, economy, etc., etc.) or even more (for French retail local stores, not online magazines - if you walked in Paris or big cities there you know), €70-€75 (like SCII and many other games - cost MORE than RRP!!!). It's very hard to get any Battle.net game key for cheap NOW (SCII/WoWz) when the games are released, what about D3 - not released, no news for date, almost nothing. If you know well-known shops (even local from your country with free shipping), then it will be better to pre-order the game (even in retail box) from there. GL.
Regards.