Everything fits in RAM if you have the budget for it.
Replacing a large number of nodes with a single machine with a lot of RAM is usually a cost savings measure rather than a larger expense (and it saves power too!), and due to a lack of communications overhead and exploitation of the fact that you now have access to all the data in one go you may very well find that your algorithms run much faster.
A distributed solution should be a means of last resort.
But seriously: the price of RAM for servers is now ~10$ / G.
It would be nice to see an article comparing all the high RAM machines side by side with specs and prices.
The largest machine I have right now will hold 512G and was a run-of-the-mill machine, it was about $5K, I'd expect the more exotic ones to be substantially more expensive but probably not as expensive as the machines linked here.
(For contrast, that $1K if you'd spend it on HP branded RAM would not even get you four 16G dual rank units...).
5 seconds of googling gets you:
http://www.allhdd.com/index.php?target=products&mode=search&...
No idea if that will work in that particular server but technically there is no reason why it should not. You can establish a relationship with a distributor to get better prices than those that you can find listed. Those 'call for quotes' things can have two meanings: you're about to be screwed or 'we will give you a better price if you promise to not divulge that we did that'.