For a 9mm single stack, the Walther has stood out to me more than any other pistol in how highly praised it is, yet how affordable too. The Sig P938 is similar, but it's double the price and for what is a concealed carry gun meant for 15 yards or less, you don't have to spend more than $400.
The only other 9mm single stack that I can think that is quality, inexpensive, and has a good trigger is the Ruger EC9s/LC9s.