The prices don't have anything to do with the free trial - it doesn't show up on the Store pages for DCS or the modules. If it works like last time, once the trial is open on Steam, you right click on DCS in your Steam Library, click Properties, and then the DLC tab. Once the trial begins, you'll have check boxes for all the modules. Click the ones you want to install, then OK, and DCS will install the trial modules. It took me forever to figure that out during the spring trial period.