The large price difference between Intel i7 3770k or i7 3770 is not because of that extra 100 MHz.
It is for that K, which means it can be overclocked heavily (About upto 4.2 GHz, quite easily) (Due to its Unlocked Multipliers).
Since, you won't be overclocking, You don't need a 3770K. Just stick with the non-K version.
However, it might be possible that you won't be thinking of overclocking at present, but your mind may change in the future. In that case, if you can buy the k version, it'll be the best option.