$900 with a tune is pretty reasonable, cheap in fact. I would guess a shop should charge around $650 for an install only... 3 days is also reasonable. Remember that most shops aren't just sitting around waiting for your car, they have other cars to work on. Most of the time, they will prep the car on one day, install the components on the next day, and tune it, the third day... while working on other cars.
If a shop comes at you with a quote of $400, they either have it down to a science, are broke and in need of quick cash, or have never done it before and don't know what they're getting into.
Like I said, expect $650 for the install and an additional $500 for a good tune (chip included).