Why are you buying arrows when you're a ranger? MAKE them!! Ivory, you are good at what you do, but here you're wrong.
FACTS
1) It costs 4gp to make 5 stacks of the basic CLASS 1 Wood Point Arrow (8sp per stack)
2) Those 5 stacks of arrows take up 4 inventory slots before you make them. 10 stacks of arrows are 8 stacks before they're made. Space-saving!
3) Those same arrows have these stats: 1dmg / 50rng (vendor bought arrows are 1dmg / 25rng)
Bonus fact 4) Silver-tipped arrows make 10 at a time, meaning that 4 stacks of mats is really 10 stacks of arrows! (These are much more expensive, though.) (Please note that only rangers really benefit from the higher end arrows!)
Here is CSA's info on how to determine arrow stats based on materials used
Here is CSA's prices sheet for fletching materials (every combination in game) (prices are the totals for 1 stack of each material, which is 5 stacks of arrows)
The initial cost of leveling up fletching past the trivial on the basic arrow can be literally nothing (trivial on those is 16, you can reach 21 at your guild master).