Originally Posted by
pesty
I did it for about 1/2 that with the wireless unit around Christmas of 2016 ordering from UK. Was just a mechanical 6870 upgrade as I already had usable crank, cassette, brakes, etc. I did have to get a long cage RD, but I was able to find a short cage mechanical 6870-SS for $30 from the same site and just swapped the cages between the two.
An "upgrade" kit is different then a soup to nuts. Is the 6870 mechanical ?, I thought that was the Di2, could be wrong.
If you have 11 spd Shimano current, even 105 (5800), the 8050 upgrade is about $1,000. $900 if you don't do a WiFi unit and extra cable for that. I just did this with a 5800 crank, b-bracket and brakes. I also had a new'ish cassette but put a new chain on. the 6870 Di2 upgrades are maybe $100 cheaper.