there are several things that you need to determine.
1. which hub do you want - the old conical solid type or the newer type ... harder to get + different price.
2. which horn button do you want. the nardi button, the old bmw button or the newer bmw logo type.
3. do you want the italian nardi, or the licensed japanese version or the chinese knock off.
2 places to check that i know of - coupeguy, crowder
crowder has the wheel for 341.60 plus the hub (with a horn ring) and the bmw horn button for $140 and the new type hub for 103.60 plus shipping. $585 +/-. no idea whether it is an italian wheel, hub, etc. or whether or not it has a horn ring. on ebay, most of the wheels are japanese made - not all. the really cheap ones or the ones that seem like bargains aren't the italian ones.
coupeguy's is a little more, but i like the bmw logo horn button.
but my 2 cents - find an old conical type of hub. they can be found for between 100 and 150 bucks.