Should i Buy SSD first or RAM for my Macbook?
Don't get a 128GB SSD. You don't want to run a 3rd party SSD on OS X without a decent amount of free space since you won't have TRIM support.

Does Activity Monitor show memory pressure? If not, I'd save my pennies until I could afford a 256GB or 512GB SSD. I've done both RAM and SSD upgrades many times and an SSD has always been by far the best upgrade in changing the "feel" of the computer.