it really depends on a number of things really. to go seriously quickly, you'll need a brushless motor and lithion ion batteries. To go even faster you'll need an uprated ESC, gears and you'll need to double up on the lithions which starts to get expensive.
typically, an out of the box brushed 22 turn motor RC will do about 40kmph. If you go full hog with all the above, then you can easily pass the 100kmph mark.
my advice is to buy local as shops are your best resource for help, advice and if you buy from a shop, they're likely to have on the shelf spares.
Feel free to PM me if you need more advice