Free: Contests & Raffles.
Bore height doesn't matter for the bullet, but if you can't adjust your cheekrest to make it the right height, you won't shoot well.I always mount the scope as low as possible, I want the bell just off the barrel. If you are buying online, find a place that does returns and order a couple of sets of rings and find the one that works perfect for you and send the rest back.
As far as I know, the biggest/only benefit of a 20moa rail is for long range shooting. Maybe I'm wrong. For a more budget friendly set of rings, I like the Burris XTR rings.https://www.cabelas.com/shop/en/burris-xtr-scope-ringsI've got several EGW picattiny rails. https://www.egwguns.com/scope-mounts-rings/standard-rifle-scope-mounts/savage/I'd do a 0moa EGW rail and a set of those low Burris rings if it was me.