Build your own it's not that difficult.
You already have the right cubby, just rip out the oem nav, decide which 7" screen system you want, wire up any buttons you need, hardwire it in and your done
I managed it and i'm a complete fool
For a nurrish nav search ebay for 7" satnav or 7" tablet, they are about £60 but a bit pants. I went for a navman panoramic, £150 and just a nav but its pretty good