There is not really a set amount but I see what you mean in relation to budget concerns. It is not the quanity but the quality of the shooting you do.
If you shoot 500 rounds with a bad draw stroke, improper sight alignment, bad grip and get bad hits you have not accomplished anything but teaching yourself bad habits.
There are no experts, but there are people that have the fundamentals of shooting mastered and that is what you need to work on. Good draw, sight alignment, trigger squeeze, follow through. With practice you will find you are a faster more accurate shooter.
As was stated get or rent a .22, cheap to shoot and get the basics down with. I have a .22 conversions for 1911 and .22 copies of my Sig 556 and MP5. This also allows me to train my wife and kids on the same weapons systems at a tenth of the price.
Take some of that budgeted training ammo and you and your wife go shoot an IDPA match. Entry fees are cheap and you will be getting experience of shooting under pressure at multiple sometimes moving targets. It will also show you if your equipment works the way you want it to or not. You will be able to see firearms and equipment that you have maybe thought about getting but have only seen in a catalog. It might not be all that you thought it was.
Bottom line is you can shoot with a small amount of ammo and get better training, if you train the right way and commit to the basics each and every pull of the trigger. Good luck.