My daughter acquired an old iPhone 4 with a screen that was cracked but still operational. She had been using the phone as-is for a few weeks, but really wanted a nice, unbroken screen. I foolishly went to another website, named after a river in South America, and ordered a cheap replacement screen. Went through the long process of my first cellphone repair and, surprise surprise, the screen was a mess of lines, static, and what appeared to be an old television with the vertical hold messed up. That's what I get for being cheap. I decided to eat the twenty bucks that this screen cost rather than attempt to get my money back through a long customer support process. I then proceeded to ifixit for some reliable hardware.
Since I had already been through the process with a defective screen, I breezed through this repair in about an hour. Like the first time, every single step was laid out, with clear and accurate pictures, in the ifixit guide. The repair was much less daunting than I had imagined.
First word of advice, don't be cheap. You're already saving a boatload of money if you're doing the repair yourself. Spring for the good stuff and purchase parts from ifixit. Everything from the replacement screen to the screwdrivers included for the repair, was of much higher quality than the half priced junk from the questionable sellers.
Second, take your time and lable everything that comes out of the phone, paricularly the screws. There were many different sizes of screws that had specific places to be returned to. Go slow and be deliberate.
And third, relax. There are a lot of little, foreign looking parts, but the ifixit guides are detailed and spot on. If you can follow instructions, you can handle this repair.