uSocial.net has offered Twitter $500,000 to place a banner ad for 24 hours.

While the sum may seem excessive, Twitter does not currently offer advertising. There is some speculation as to the authenticity of the offer.

“While half-a-million dollars may seem like a large amount to invest in one banner for one day, we believe that the investment will be more than worth it,” said Leon Hill, CEO of uSocial.net.

uSocial.net has generated some controversy in the blogosphere around its service, which sells Twitter followers in increments of 1,000, 2,500, 5,000, 10,000, 25,000 and 100,000. Prices start at $87 for 1,000 followers (‘delivered’ within seven days) and rise to $3,479 for 100,000 followers (‘delivered usually’ within 365 days).

The company purports to match followers with profiles aligned with their interests. It then sends messages to potential followers suggesting users they may like to follow.

It’s up to the user to follow them or not, said Hill.