The cheapest .. any Elm327 Bluetooth/wifi to use with an android phone. 5-10 euro.
The best cheap diagnostic tool you can get is a USB Elm327 + MultiEcuScan.
With this combination you can do almost everything the dealer can.
You still need to have some troubleshooting skills, but the info is out there. Multiecuscan also gives you the possibility to plot graphs -really useful.
Alternatively, search for "PIC18F25K80" to get a correct working ELM327 interface. I've tried a few Chinese clones, and majority of them doesn't work with this car.
You only need the Yellow adapter to access all the ECU's, but the price difference is not that big for one compared to 4.
For desktops, you've got MultiEcuScan and AlfaOBD. I prefer MES over AlfaOBD due to user friendliness. For mobiles you've only got one choice - AlphaOBD. Demo version gives all the necessary tools to read/clear faults and see values/parameters. But you can't invoke any procedures like clutch drain or depressurization.
Personally I wouldn't get a scanner if you have a laptop. Get a copy of MES: http://www.multiecuscan.net/ and follow their advice on an interface cable