I am happy with the route I took in pistol purchases, but if I was very limited I'd start with something like a Ruger 22LR. What you suggest in that post is something I want also especially that I am considering some form of competition. I will probably get a CZ Shadow 75T, and the 22lr conversion kit, except no one carries that model, and as with other manufacturers I like, the availabilty is ummm, "lacking". I handled a CZ "Canadian" which was nice, but I didn't care for the gawdy "hey look at me" red grips - an expense in useless affectation, when I'd rather have a wood or even plastic grip that fits my hand with a fully adjustable rear sight... It's said that manufacturers produce what people want - If that is true, people are very impractical. Anyway, sorry about the rant, but what you mentioned is a viable option - You will have a reasonably affordable gun to shoot affordable 9mm rounds, and the ability to switch out to a "half" priced gun that shoots cheap 22lr rounds and really, the latter is the best choice for developing technique and a 22 will remain the most popular round for continuation training. It seems my rant is not entirely correct given that last sentence.
If you elect a two separate pistol path, I expect they cost the same as the conversion kits... a reasonably used 22 would cost less. I paid around 250.00 for my Ruger Mk1 Target pistol. Unless you get a total dog, you probably will be content with what you do get. If ammo affordability is of great importance avoid the larger calibers. 9mm, 38 special (if you desire a revolver) and 22lr are in descending order, the cheaper options in ammo.