Well, Here's my guide on how to get 99 fletching.
1-5 Fletch arrow shafts, 79 logs are needed.
5-10 Fletch regular shortbows, 154 logs are needed.
10-20 Fletch regular longbows, 332 logs are needed.
20-25 Fletch oak shortbows, 205 logs are needed.
25-30 Fletch oak longbows, 583 logs are needed.
30-40 Fletch willow shortbows, 446 logs are needed.
40-50 Fletch willow longbows, 1545 logs are needed.
50-55 Fletch maple shortbows, 1307 logs are needed.
55-65 Fletch maple longbows, 4855 logs are needed.
65-70 Fletch yew shortbows, 4270 logs are needed.
70-99 Fletch yew longbows, 81979 logs are needed, This method you will also string them.
This way will cost you around 50m, But on 8-10m is needed, From 1-50 I do recommend cutting your logs if you can't buy them, Rather then making money for them if you really want 99 fletching.