.40 or 9mm

Can you please provide some additional information.

Why is the .40 cheaper than the 9mm?
- Is it used?
- Does it lack the German proof marks?
- Do they both have the DA/SA trigger configurations?
- Do they both have stock sights?

How  much cheaper is the .40?

A couple of things to consider...
- Typically, 9mm ammunition is substantially cheaper than .40 S&W.
- The 9mm is usually easier to shoot well than the .40, especially for the novice.

-I don't mean this to sound offensive, but I think you are approaching your purchase incorrectly. Comparing the price of a new P99 in 9mm and a used P99 in .40 S&W is like comparing apples and oranges. I understand that price is important, but what is more important is getting the gun you'll like to shoot.

As you mentioned in your post, you are new to the handgun world. It sounds that you may not have the experience with both calibers to make the choice that will be right for you. There are several things to consider: what the calibers can do (i.e.: stopping power), what the trade-offs are (i.e.: ammo costs, capacity issues), and most importantly which caliber works best for you as a shooter (i.e.: accuracy, since some people do better with certain calibers & recoil issues).

There is no substitute for time on the range with the caliber and if possible with the actual model you are considering. (I drove to a range that was over an hour away from me to try the P99, before buying one.) If you cannot try a rental and you are going to buy blind, you really have to make the decision based solely on which caliber you perform better with. Again, this is where being new to shooting may put you at a disadvantage.

-What I'd suggest, is that you go to a range, rent two guns that are the same make but different calibers i.e.: the Glock 17 (9mm) and the Glock 22 (.40 S&W). Try them. Since they are the same size and weight and will have the same trigger pull (as each other, not the P99), you should get a fairly good idea of which caliber you prefer and if you feel good with stepping up (in power and recoil) to the .40 S&W.

-With that said, I do not think you can go that wrong with a P99 in either caliber. They are great guns. However, the core of your decision should hinge on caliber preference not which model is cheaper.

Good luck-