Not much going on in here so I might as well throw this question out:
If you want to buy for a large amount, say between $ 50k and $ 200k, what is usually the be way to buy them on the exchanges? I guess somekind of limit order would be preferable?
First off, don't post the question on these forums
.
But seriously, that's not a huge amount -- ~500 to 2k coins at today's prices. The key questions here are:
What's your starting point? (are you verified on any exchanges)
What's your timeframe?
Is this potentially a repeat thing?
Are you interesting in cultivating new exchanges?
The best short-term strategy that does not involve manipulation would be to purchase on multiple exchanges simultaneously. You could probably fill that order on bitstamp, btc-e, campbx and only drive the price up a buck or two. By using multiple exchanges and buying as soon as the money hits your accounts you minimize exchange risk. But that presupposes you have accounts in these places.
If you had only one account (at bitstamp, say) and a longer timeframe, I'd break the purchase into 3-4 smaller wires to minimize exchange risk. That would also space the purchases out so you'd likely not move the market.
But if you anticipate repeat business (and judging by your website, I'd guess you do), I'd register and KYC with every exchange I could find, including one in China. Because you never know when an exchange could disappear... and if you are filling whale orders you may need to produce on a short timeframe.
Finally, you might want to create a relationship with one of the new exchanges that have been recently announced and risk a few $ filling out their bid orderbook. I'll bet a phone call could get you really low fees...