A long time ago, bank checks used to look like normal deeds. The gods changed them to gold to help prevent scammers from closing a window and replacing the white check with a normal deed. It used to be a very popular scam and many a person fell to it.
White checks could be made in any amount (and the gold ones still can) though a bugged system. Desirability is based on the number when it comes to checks. Even round numbers are desirable like 100, 500, 1m along with 69, 666, etc for particular collectors. 1 would be desirable to as it stands out and even though many were made it is one of the more desirable numbers. I'd estimate it to be worth about 1.5m. I don't see white checks usually below 750k personally, but I've seen them sell up to 2m under optimal circumstances.
On a side note, the above also goes for the old multi-gem jewelry. Oddball numbers don't sell for very much, even if they are a higher number. For example, 100 gem jewelry will almost always sell better and for more than one wth 165 gem.
Hope that helps.