My advice - keep away from the "after dinner speakers circuit" and save your money!
Instead, if your audience is predominantly light blue (and/or young) I can strongly recommend you inviting one of the many current Army GC, GM, MC, CGC, DSO etc winners (and not necessarily the higher ranking ones either!) from either Iraq or Afghanistan. The reason I say choose Army is, having been in the audience of a couple of these presentations/speeches recently, it is truly humbling (and indeed frightening!) to hear first hand what modern land warfare is all about (and before I get flamed I know that plenty of light blue have been, and continue to be, in the thick of it but it's always good to hear 'the other point of view' if you are ever going to understand each others problems!)
If your audience is predominantly of the older generation then I would suggest you also invite (for free!) a good number of the young Toms as well and spread them amongst the dinner guests. You'd be surprised how much the older veterans are keen to hear about the modern battles as vice-versa.
Most local units will find people willing to do this for nothing more than a free meal (a few drinks after!) and overnight board.
And the younger the after dinner speaker the more chance (hopefully) he'll still be around come November!