What you can do is just buy the bow, SP farm until the right amount that you needed, then resell. Theres usually someone looking for a level 16 bow anyway, and if the critical is good then thats a + for you. After selling ur bow, you can buy ur wolf easily. Oh and since ur at level 20, you should re-think about SP farming, I heard its better to do so at level 16, or at a higher level.
Hope this helped.
Oh btw, your wolf gets their own exp. and you get your own. It doesn't split from the amount you would normally get or anything, or at least im thinking that because my friend's wolf gets their own exp., while he gets his own. So if you kill something with your wolf just by your side and not attacking, both of you get exp.