I know this isnt what you want to hear, but id save it if I were you. Bandos is cool looking, but for slayer, all you need is barrows armor really, and for the most part barrows is even better, unless you have 99 def and uni and such. Also, 50m is great pray xp, but not really enough to get from 70 prayer to the real goodies.(soulsplit, turm)
So for now, id save until you are 100% certain on what you want. Don't get me wrong, it is your money and prayer and bandos both have their benefits, but that is just my opinion. Like you said, you feel like you have everything you need atm.
Hope this helps