No matter what you do get it - you have to do this every year to maintain it. That is unless and until you reach 1M Miles on UA or a similar LT status with another *A program.

The 'easy to get' SAG status options are dwindling - OZ will be gone soon. Some are left and some don't require flying that specific airline either - it will require a lot of flying though.

I'd check the airports you most need these for and look into CCs like Amex Plat or Chase Sapphire - they might get you to 80% of your lounge needs w/ a fairly modest expenditure.