Just checking see if any memeber done this and how hard is it to retro fit head up display ? i saw they selling the unit itself on ebay now and wondering if you that's all you need to do it or you need to change the dash as well ?
Sounds like a very expensive job. You may have to replace to entire dash, and I'm pretty sure HUD equipped M5s have a special type of windshield, so that would need to be replaced as well. Honestly, it would probably cost you less and be much less of a hassle if you just sold your M5 and got one with HUD (if you feel it is an important enough option).