For the heck of it, relevant quotes about numbers concerning Saruman's thralls...
Chapter 7, Helm's Deep
"He that flies counts every foeman twice, yet I have spoken to stouthearted men, and I do not doubt that the main strength of the enemy is many times as great as all that we have here."
"The hosts of Isengard were advancing in silence now. Their torches could be seen winding up the coomb in many lines."
"Hundreds and hundreds more were pouring over the Dike and through the breach."
When the moon's sinking...
"Ropes with grappling hooks were hurled over the parapet faster than men could cut them or fling them back. Hundreds of long ladders were lifted up. Many were cast down in ruin, but many more replaced them, and Orcs sprang up them like apes in the dark forests of the South. Before the wall's foot the dead and broken were piled like shingle in a storm; ever higher rose the hideous mounds, and still the enemy came on."
(Well, Turbine certainly got the bit about the grappling hooks right in the BBs...)
"Between the Dike and the eaves of that nameless wood only two open furlongs lay. There now covered the proud hosts of Saruman, in terror of the king and in terror of the trees. They streamed down from the Helm's Gate until all above the Dike was empty of them, but below it they were packed like swarming flies."
Chapter 8, The Road to Isengard
"No Orcs remained alive; their bodies were uncounted. But a great many of the hillmen had given themselves up; and they were afraid, and cried for mercy."
Rohirrim corpses were piled in two mounds, but "the Orcs were piled in great heaps".
Chapter 9, Flotsam and Jetsam
(As told by the Hobbits)
"All Saruman's people were marching away. --- He emptied Isengard. I saw the enemy go: endless lines of marching Orcs; and troops of them mounted on great wolves. And there were battalions of Men, too."
"Well, of all sorts together, there must have been ten thousand at the very least," said Merry. "They took an hour to pass out of the gates. Some went off down the highway to the Fords, and some turned away and went eastward."
"As soon as our attack began, the few remaining rats in Isengard started bolting through every hole that the Ents made. The Ents let the Men go, after they had questioned them, two or three dozen only down at this end."
As an aside...
"But arrows are no use against Ents. They hurt them, of course, and infuriate them: like stinging flies. But an Ent can be stuck as full of orc-arrows as a pin-cushion, and take no serious harm. They cannot be poisoned, for one thng; and their skin seems to be very thick, and tougher than bark. It takes a very heavy axe-stroke to wound them seriously. They don't like axes. But there would have to be a great many axe-men to one Ent: a man that hacks once at an Ent never gets a chance of a second blow."
"And anyway (Saruman) did not understand (the Ents); and he made the great mistake of leaving them out of his calculations. He had no plan for them, and there was no time to make any, once they had set to work."