How much membership should I get for the best price?

Ive been playing a bit, got my magic, defense, strength and attack almost 40 and prayer is 33 with ranged at 20. But looking at the “view” menu in skills, after level 40 theres not a whole lot left so I want to get membership and my birthday is in a few weeks. Im a noob but im enjoying it, I watch tons of series on YouTube about it doing different challenges. I wanted to try for the fire cape eventually.