That is a common piece of advice, buy once cry once, I see it in every gun forum, when I try and look for a cheap sight pusher, or screwdrivers, punches, etc. When you are dealing with Higher quality Firearms especially.I have tried one of those with little success. My advice- buy once cry once. YMMV.......
If I were not going to invest in one of the best like an MGW, I would just stick with a decent vise with good padding and grip and just use brass and nylon punches made for sight pushing. Lots of tape to protect from slips and I would not start with an expensive fire arm.
One problem I know you will run into is," that one sight that slides a little and then locks up." That is where a top quality sight pusher is going to help with that head ache. How much does a slide replacement cost when you ruin it. Guarantee you will run into that deal if you change more than two sights on guns. Murphy's Law of if it can happen it will happen.