You mention combat, and yet speak of discount deals in the same question.
If a major agency or the military adopts a handgun for combat the ammunition it uses will become more widespread and solve any concerns about availability and price.
So price of ammo in terms of combat thinking is relative only to the the amount of metal required per round.
So are you really asking what is best for you, what is best for a civilian, what is best for police, or what is best in actual combat?
As a civilian a light weight polymer pistol that uses widely available ammunition might be a great choice.
For a military where soldiers fall, crawl, roll etc over thier weapon, I certainly wouldn't want a plastic gun. In combat weapons take abuse above and beyond the mere operation of the weapon. Something highly modular is also helpful since it allows both quick adaption of the weapon, and the ability to cheaply and affordably replace a section of the firearm rather than say the entire frame.
In combat you want different things from different weapons. Since a handgun in combat is a secondary weapon you must think of what its uses will be. It will be restricted to FMJ rounds in the military which changes the choice. A larger diameter bullet becomes more important without expansion. Yet if they have body armor a small diameter hole with more energy becomes more effective. If you expect most of the enemy to have body armor rated to stop pistol rounds (and trauma plates in spots for some rifle rounds), then a low capacity high power backup if you ever actualy do need your pistol instead of the rifle you always carry might be worth considering. Loaded with AP rounds of course. IMHO that beats the go smaller and smaller philosophy you see in the ammunition designed for PDW's which have proven to be unreliable manstoppers with or without body armor on the target. That way when your rifle is down you are not left plinking at them ineffectively while they return with rifle fire. (Totaly different from current practice of using a 9mm round and just planning to basicly never use it, or a .45 to only face jihadists without the armor most professional armed forces wear now.)
Now as a civilian or police officer things are totaly different. The handgun is in fact the primary weapon most of the time, and you want medium capacity and medium power. More rounds than you need, and sacrifice power for controllability and followup shots. Lighter weight is more important than absolute durability as well since you shouldn't be rolling over, and falling down on, and generaly abusing the weapon. A assailiant without body armor is more likely than one with. Expanding ammo means the bullet diameter upon firing is less important than the diamter after expansion and total energy. So with both the use and the targets being different, the ideal characteristics are totaly different.
Primary weapon vs secondary weapon, armored vs unarmored, weight vs durability, modular vs streamlined, expansion vs FMJ or AP.
So what is really your question? Best handgun for what? Does combat really have anything to do with the information you seek?
The best "combat" handgun is not the handgun I would want to carry for use in a defensive firefight as a civilian.
The best civilian handgun is not one I would want soldiers on a battlefield to have facing other soldiers in combat.