[zalagan]

Most extended storage features are easy to retrofit yourself but some are very expensive as parts:

Rails and lashing eyes - requires new reversible floor, very expensive but rails just bolt in
Extra nets - seat back nets not worth the effort and risk of damaging seat back panel clips. Others cheap and easy to do
Elastic belt and extra hooks & eyes - easy, cut-outs in trunk side wall trim are already marked on inside, just need a good Stanley knife to open up holes. Low cost parts. Some screws needed
Storage box under light switch - others have done it, see other threads. Inexpensive but potentially disastrous DIY if you get it wrong. Only possible if you don't have HUD or other electronics in the dash void
Cup holders in rear seat - again, expensive parts
Extra power sockets - needs wiring to fuse box - not worth the effort

I miss the old E83 where the wiring harness was common and spare connections were neatly wrapped in foam and tucked under insulation ready for when you wanted to retrofit something. Who cares what it weighs - bring back old BMW engineering that allowed retrofitting!