First of all, the work needed depends on the way in which the final velocity is reached. If you write the expression for the work done by the drag force you obtain
$$W=-\int F ds = -b \int v^3 dt$$
and it's easy to see that if the object is carried to its final speed in a very short time $W$ can be arbitrarily small because $v$ in the integrand is always less than the final value, and the integration time can be reduced at will.
As a concrete example, let us suppose that the object is accelerated by an engine which has a constant power $P$. We can write
$$\frac{d}{dt} \left(\frac{1}{2} m v^2 \right)=P-bv^2$$
which can be explicitly integrated:
$$\frac{m}{2} \int_0^{v^2} \frac{dv^2}{P-bv^2} = t $$
which gives
$$\log \left( 1-\frac{b v^2}{P} \right) = -\frac{2bt}{m} $$
and
$$v^2 = \frac{P}{b}\left( 1-e^{-\frac{2bt}{m}} \right) $$
The maximum speed that can be reached is $\sqrt{P/b}$. Now, let us suppose for simplicity that $P$ is large compared with the power of the drag force. In this case we can expand the exponential at the first order obtaining
$$v^2 \simeq \frac{2Pt}{m} $$
The work done by the drag force can now be evaluated using the integral in the first equation,
$$W=-b\int \left( \frac{2Pt}{m} \right)^{3/2} dt =-\frac{4}{5}\sqrt{2} b t \left(\frac{P t}{m} \right)^{3/2}$$
which can be expressed as a function of the speed
$$W = -\frac{b m}{5 P} v^5$$
As expected from the general initial discussion, $W$ can be reduced by increasing the engine power $P$.
Best Answer
This idea may contribute to increasing or decreasing downforce, depending on the profile of the blades.
You don't give a speed range, and I'm not sure how this would compare with the downforce generated by underbody fairings, but it's not allowed under FIA rules.
The Brabham BT46 fan car was banned (as it was too damn good), and if you like you could compare the angular velocity of the car's 4 wheels with that of the fan. I think this is a good argument for saying you might be on to something, but although it's easy to work out the wheel speed, I can't find anything on the angular velocity of the fan.
This is getting into EngineeringSE territory, but as I am an F1 fan (sorry) myself, I can't resist a picture to allow you to compare diameters.
The FIA ban might suggest that it is a potentially effective idea, but that it is also inherently dangerous as, at high speed, you don't want one corner of the car to unbalance an otherwise symmetrical distribution of downforce if the wheel blade profiles are not matched properly.