"EDIT: Instead of donating for upgrades of the item u have, they could implement an option that if u have downed a boss and got the achievement that could drop the item u want, u could go directly into the marketplace and buy said item at the extended cost so u dont have to wait until next raid and hope it drops."
This is an extremely awesome idea dude. I myself donated.. like HUGE amounts of cash on Molten/Warmane, but I don't want that Pay2Win on Lordaeron. After all, on Deathwing/Ragnaros it's more of a Pay2Keep-up rather than win.
The achievement requirement would let impatient players (no offense here of course) get their desired gear without the frustrating "It didn't drop" (although immersion fans will only want it that way), the server would get many contributions (since still many will want it as fast as possible) and nobody could complain about Pay2Win.
If the server needs more contributions, consider making any pets/mounts available for coins (always wanted this Qiraji mount sooo hard...). This is cosmetic and won't affect gameplay. Although it might be immersion breaking having all kinds of mounts you didn't do anything for but pay, it is still MILES better than being able to buy higher-tier gear.