Ok $420 is something that would make a big difference, I agree
Yep...
Now, all that said, you do need to factor in sales tax depending on where you live and the current laws. Particularly if you went to college in a different state from where you currently live. Some (many?) colleges will sell to alumni under the education program, which not only involves $$$ off MSRP, but can also entail substantial savings on AppleCare+
In my case, I bought my MBP15 through my old undergrad school during the back to school promo -- but looking today the MBP15 pricing is $150-200 below MSRP, and AC+ for MBP15 is $259 ($120 savings) -- net is that refurb+AC+ is still ~$50 more expensive after tax than buying from my old college's campus store.
Alternately look at the various deals listed at Apple Insider --
https://prices.appleinsider.com/15-macbook-pro-with-touch-bar-mid-2018
Up to $300 off depending on config, for brand new, with no sales tax if out of NY/NJ (depending again on your current local laws regarding such). Downside of course is much more limited returnability of non-defective units, so be sure you know what you want.
One other factor to consider -- some credit cards (Citi and Amex to my knowledge) offer extended warranty protection, which actually becomes active after AC+ runs out. What was unclear in my research though was whether those programs applied to refurbished equipment. Depending on whether you have one of those credit cards and your expected length of ownership, there may be value to you in ensuring your coverage is clear and not ambiguous.