There isnt any difference really in what it does, but you can supposedly take significantly less to get the same benefits. I have taken both for extended periods of time and noticed no difference in performance (which is the point) but i was taking less creatine per day with the kre-alk than with monohydrate.
Not sure what brand/where you buy it from but the kre-alkalyn i was taking wasnt much more than monohydrate. If you are taking it in the same quantities as monohydrate then i could see it costing significantly more.
The main reason i took the kre-alk was to minimize water retention, i look bloated enough as it is from my current bulk diet.
Either way its not like one is far superior than the other. They both provide the same benefits.