When withdrawing something from the bank or making something like in fletching, you should have an option on right click to the last number you put in x. So like 28. Yeah lol
This isn't a feature on Rs07, so I don't see why we should have it added in-game.
Here is an alternative way to train your fletching on alora:
Buy Broad arrowheads and unfinished broad bolts from the slayer master 'Nieve' at home, for 96 Coins each.
This will be the way to go from 55-99 fletching, its extremely fast and doesn't cost a lot.
55-99 can be done within 15 minutes.