CO2 scrubber is the easiest if the purpose is the raise pH alone.
Kalk or two part have some impact, but none of them can only raise it a bit, 0.1 or less. For best effect it needs continuous slow dose, which only high end doser can do.
Refugium is easy to crash if it actually works well.
Air exchange unit cost thousands, and depends on your outdoor CO2 level.
CO2 scrubber cost less than $100 (TLF Phosban reactor). Media cost for my 180 is about $100 a year when buying the 5 gallon bucket. It can easily raise pH by 0.3+. Mine went from 7.8~8.0 to 8.2~8.4. You can start with $100 to try it out.