As far as the firearms you've listed go, the Ruger LC9 is going to be by far the cheapest, but just as well, it's also a very nice carry firearm which only weighs 17oz, holds 7 rounds in the magazine, (with factory 9 round extended magazines available) and is a good shooter.
The Ruger EC9s (which is just the "economy" version of the LC9s with fixed sights) retails for $249, but can often be found for $200, or even as low as $175 in used condition.
Otherwise, the M&P series often gets factory rebates around the holidays, and police trade-ins of the M&P40 1.0 show up periodically for $300 or less depending on their condition.
Another option is the less expensive S&W Sigma series of firearms, which have seen limited use by Law Enforcement, but have long since become a value priced firearm, so they're more of a civilian firearm these days. Still, they can be had for very cheap if you shop around. The modern iteration of the Sigma, known as the "SD series" can be had for as little as $300 new, often with $50 rebates, and used models go for around $250.
I myself actually bought a used LNiB Sigma SW40VE for $199 a few weeks ago. The Sigma series got a bad rep for the original 1994 SWF models being unreliable, but any of the later models made from 1999 onwards are fire, although they do have heavy 10-12lb DA triggers which some find objectionable. However, there are many ways to reduce the trigger pull if you find it too heavy. Personally, as someone who is used to heavy DA triggers, I have no issue with the Sigma's trigger.