At a guess without seeing it, you would need at least a scuttle end panel, closing panel and wing. The reason i say scuttle end panel is there is every chance that the rust will have eaten that away too under the top join of the wing.
If you are on a tight budget now but may be able to afford the repair in the near future, then you could cut out the rust and repair it with fibreglass matting and resin but this would be a very last resort and i do not recommend it as the rust will continue its dastardly plan of destruction underneath.
Pattern wings are not expensive. Have a shop around, you may be surprised.
A picture speaks a thousand words though.
Ben