Here is a link to a video that shows how to replace the LCD screen and Digitizer (touchscreen) on your phone.
Here is a link to just one supplier of the part. It is not a recommendation to use them. It is shown to give an idea of the cost of the part. There are others online that may suit you better.
If you find the repair too daunting to do yourself then I recommend that you contact 3 reputable, professional mobile phone repair services and ask for a quote for a repair. I suggest 3, that way if all the repair estimates are close you will have a truer indication of the cost of the repair. You should already know the cost of the replacement part.
Hopefully this is of some help.