100+ people complete thru-hikes every year, so it is very possible to do so. Of course, 100+ people fail to complete an intended thru-hike every year, as well. To make it all the way border-to-border you need to be very determined to do it, be reasonably fit before you start, and have the right footwear.

Many successful thru-hikers wear trail runners, some wear boots, but wear whatever fits you best. Foot problems probably get more people in trouble than any other single item, especially during the first month.

As far as what "should I go all out and purchase no matter the price?", I'd say your backpack. If you don't get the right one, your shoulders, back, and hips will be miserable. There are many fine packs in the $150-$250 range. For both footwear and packs , find someone who really knows their stuff and can make sure you get the right fit. The usual advice is to buy your pack after you get all your other gear and I think that's good advice especially if you can't afford to buy several of them before finding the right one.

Good luck with your planning.