If you get everything by yourself = String and Alch.
If you buy everything you get = Just Buy yew and flax, then make bows and sell.
Because if you buy everything and you alch, you won't make a really good profit:
1. Yews = 250-260ea (I think.. Didn't fletch for a month)
2. Flax (or BS)= 100-110/160-180ea
3. Nats= 320-330ea
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Total = - If you buy flax= around 78-98gp profit per bow.
- If you buy BS= almost 0gp per bow.. maybe 20-30gp per bow.
Conclusion: Depends if you want to get XP or MONEY
Edit: But if you get everything by yourself, you'll get xp AND money

but it's going to take more time.