I'm not certain on the equivalents for pounds or euros, but if you pay in US dollars, then one crysta is equivalent to one cent. So if you find a listing for something that shows the cost in dollars, then just remove the decimal point for the number of cents, and that's how many crysta you need.

If the price hasn't changed since I last saw it, it's 1999 crysta for either the ARR or HW upgrades, or a bundle for both of them at 2999.