Interested in Modding, I see. We have the source code for Enemy Engaged - Comanche vs Hokum available here on SimHQ, I've been modding it recently. It's probably the newest helicopter sim available where you can get at the source code. It has a following similar to Falcon-4 since the engine includes dynamic campaigns, an ever evolving battlefield. Take a look in the EECH / EEAH Forum and go to the link in the header to get to the eechcentral Modding downloads. (
http://eechcentral.simhq.com/ ) There are 9 fully modeled helos for you to fly into combat. The base game is about $5.99 on GoG Games, the mods are free. This is a sim, not an arcade game, so expect it to take some time to learn the systems on your helos. I just added in working Altitude Hold and Hover Hold functions, so the helos are much easier to fly now, you can skim the treetops with ease. You will find the Hover mods download in the forum. Get the Mi-28 Gauges mod from the forum as well so the Havoc cockpit gauges work.
If you don't mind only one or two helicopters, DCS World has the best graphics. It has the Russian Ka-50 Blackshark, the Huey, the Gazelle, and maybe one other helo available. You pay for each additional module in the sim. These helos are extensively modeled, every button and switch on the console is live. There is a mode where you can simply jump into a running helo and take off, so you don't have to use a start up checklist every time. DCS World is a more expensive route, but definitely worth a look. I just checked and they have a Helicopter 4-Pack available until Sept 30th 2018 for $70.