From looking at the O.R., Price had two division with him at Iuka, Little's (Hebert's) and Maury's. Their estimated sizes going by brigades was between 1400-1700 men per. Little had four infantry Brigades and Maury had two Infantry, one cavarly fighting as infantry and one cavalry. (plus artillery, misc. cavarly, and train) So my estimate would have been at a minimum about 9,800 men and a maximum of about 12,200 men under General Price at Iuka.
Little's was the only one engaged in front of Iuka, Maury's performed the rearguard action.
Maybe Price wanted to join with Van Dorn more than he wanted to go toe to toe with Rosecrans at Iuka? But he stated he when he found out that Rosecrans had 10,000 men at Iuka he immediately set off with his army to meet him. This was an over statement, since the garrison of Iuka evacuated when Price showed up must have been much weaker. This tells me he wasn't affraid to take on an equal sized force.