I only have one tip. In my area , Baton Rouge, LA. , there are two or three gun shops . If you purchase your sights from them they will install them for free.
But I can get them cheaper on line you say....

So in the long run how much cheaper is it going to be....?

So check some of the local gun shops , and see how much they charge for the sights and installation, you will only have to buy the new sights once and you will not have to buy nylon punches or brass punches .
If the gun shop screws the installation up....they pay for it not you !
I learned a long time ago that at times it's cheaper to let a professional do it.
Gary