Reality of buying online money wise

So many offers online from different websites offering guns 2-300 less than what they are sold across gun stores jn nj (prices for nj still need to add tax and nics)

Ive seen a lot of offers at even 50% off, but what is the reality once you add FFL transfer fee and maybe magazine modifications?

Seems like there is a huge difference in prices from actual gun-shops in nj and some people here claiming they are ffls.