How many 100’s, 1000’s, millions do you need?  

Extruders have a set-up charge for the die, etc. and usually use billets of 400 pounds minimum.  Some of the larger ones have pretty large minimum orders, e.g., see
http://www.accumetinc.com/alextrus.htm (min. 1000#, but surcharge < 45000#)
http://anaheimextrude.com/extrud03.htm (smaller minimum, maybe 400#.  Site illustrates the overall process)
http://www.argylein.com/  ;(‘no order is too small’).

I might chance a guess of $400 set-up, $1000 aluminum cost, plus delivery, for a minimum.  The price might be $5/# for 400#, dropping to $2.50/# for 50,000#.

If this is small quantity item, have it machined or rolled from billet.  For a simple, solid geometry, rolling is much cheaper than extrusion.

Thanks!
In your opinion, would extruding about a million of these blocks cost around $1.50-$2.00/#? Or would the cost increase slightly as you ordered more than a certain number?

I noticed that you posted elsewhere info that these are finned heat sinks.  For a large enough quantity, extrusion is definitely a viable process.  The tooling cost might be higher than I earlier estimated for a rectangular shape, but it would be ameliorated over 1000's of parts.
As I have only purchased extruded lengths of bar, can't give a better idea of price, except the general note that price per pound decreases with quantity.

Contact some extruders; you may find one with a similar die who can quote you right off.

Good luck,
Ken

Note that the style and complexity of the shape, the alloy, temper and finish will affect the final cost also.  I have designed many extrusions from 3/8" channels to 8" I-beams, some hollow, semi-hollow and solid.  A finned shape will cost more to extrude although careful attention to details that affect extrudability and the likelyhood of waste can minimize the extra.  How tight are your toleances?  Tighter tolerances mean increased cost.  Cost increases for semi-hollow and more for hollow parts.  Avoid a shape that has thin parts as well as thick.  Some shapes are better made at specialty extruders.  The Aluminum Association has documents that help you design extrusions as well as standard tolerances and engineering data.