If you do go down the bike upgrading route (it will be more for fun that performance for us mere mortals) then KCNC/ Mt Zoom/ generic Chinese carbon stuff is light, strong and cheap. There is some really good light stuff out there nowadays without having to spend a fortune. Ralphs and the wheels Njee suggests are a great foundation too. Clee Cycles, XC Racer, R2-Bike and similar shops will give you a good feel for the weight and cost of various shiny parts 😀
Since investing in a decent light bike I can tell you one thing… the painful, steep, long hills are still painful, steep, long hills! It must help slightly but it doesn’t feel like it sometimes!