If you referring to outside shop , well they might be cheaper but do not forget u will lose the water resistant feature if u do at outside shop. Also workmanship might be bad and U end up with a faulty phone that give u more problem and waste more time making return trips.
Second if u have a crack on the screen so meaning u had dropped the phone and it will have cosmetic damage so I will go for the 1-1 replacement which is only $148 which is way way cheaper than the $500plus(price is for ip6/6s , not sure of ip7 price)
TG protect the screen 100%?? I know of a few cases that the TG is intact but the screen cracked for Iphone after dropped with casing some more. Nothing is 100%
It is a very subjective debate on to get AppleCare+ or not and is it worth it?!?!
As long u can afford the AppleCare+ and u can get to use the phone without worrying too much then why not?
hmmm..does repairing a screen really cost more than $228 + 42 = $270?
BTW, most people get tempered glass protectors nowadays... is it really still a big risk nowadays?