I managed to buy two (used, genuine) replacement front wings for my 2003 E46 Touring (on ebay). I paid £55 each. Having them fitted, treated underneath
with rust inhibitor, painted and faded into to rest of car's colour (even though they were the same colour), and the rear wheel arches ground down
filled, repainted (after rust inhibitor applied) was £660 inc vat. I was happy with the price and the job they did.
The rust may come reappear, but for the time being I'm happy with the way the car looks.
(Happy to supply photos).