Did you try a command line execution of DCS_updater.exe with the "repair" option from the dcs directory ?
If i'm not mistaken, DCS does not mess with registry. Lauching "DCS_updater.exe repair" from the F: drive instalation ("<directory of your DCS>\bin") Should target the active directory and not the default install.
If you need help with command line, you can PM me.
P.S. Couple of hundred dollars for a full DCS install. That's quite a huge ISP cost :(
