no, it's not. apple pretty much changes all components when it develops the next model.
an iphone 8 camera will not work in an iphone 7. chances are the flex cable and plug are different so you wouldn't even be able to make the connection.
for pricing, check out
mobile sentrix
injured gadgets
wholesale gadget parts
these are all pro suppliers, have excellent products and great post-sales support.
if you're really on a budget, or just want to go cheap, give ebay a try.