I'm not going to bother arguing with those who think .40 is "obsolete" or "dead" because it seems twice a week on every gun forum any time .40 is brought up the same words used by 9mm and .45 fanboys is the same.
It's not hard to find .40 S&W pistols if you know where to look online. Gunbroker is chock full of Glock 40s among others, but if your goal is a cheap .40 that's cheap because it's .40, I think the prices have gone as low as they're going to and the closer we get to the election, the more the prices are going to go up.
I hear you on getting a steel frame .40 that's DA/SA or DAO tho, I'm looking at S&W and Kahr online and the prices are hard to believe for what are high quality pistols. Given I have 3 guns in .40 and a bunch of ammo, I see no reason to dump them and switch to 9mm. That's not to say I don't have 9mm guns, I do, but when it comes to a steel frame pistol, I see no reason to buy one in 9mm over .40, 10mm, or .45. The recoil with 9mm in poly frame pistols is low enough.
Speaking of low recoil, I think with all the cheap .40s around, what would become very popular is low recoil .40 ammo using projectile weights similar to 9mm. The overwhelming majority of .40 ammo is 165 and 180 grain, there is some 135 and 155 grain ammo out there, but it's not common or cheap, the 135 grain ammo is usually $1/round.