[ctuna]

Technic has three levels of Base system harness depending
on how far you want to go.

Bimmertech and Bavsound have plug and play setups using
the Helix 86dsp and BMW7 dsp amps respectively.

I know bimmertech had a base system plug and play kit not
sure about bavsound. Includes harness.

Pretty hard to do absolute easy plug and play with a base system
because you need harness to the trunk and maybe coding to Hi Fi.
I believe this is included in the Bimmertech kit.
You should also at least get a new set of speakers for everything
up front.
There are lots of plug and play speaker sets for the front's now.
Jehnert , Helix Match ,Rockford Fosgate, Audio Systems see audio build
thread speaker list.

I would go with the Helix Match speaker sets for the front's
Next level would be Jehnert xe 200's for the underseats
and Morels for the doors.

Price wise 700 would be low for kit that probably would only barely
cover the amp/dsp and then another 500 to 700 for a set of quality
front speakers.