Hi Mate,
Just a thought with regards to your rust in the boot, is this the notorious corner where the exhaust peg is located. As this seems a bit of a hot spot for rust and is worth checking sooner then later - unless you want to be dragging your exhaust home.
If this is the where the rusty area is then some garden wire could be an extra addition to your cars tool box.....
If this point goes it can lead to some drastic welding being done in order to repair the corner and replace the exhaust peg, as the need to grind back to good metal can lead to quite a reasonable hole being produced.
The rust seems to vary and no one model seems to be worst than others, from what I've gathered anyway.
Likewise, its worth checking this peg area and if everything is fine then a regular clean to keep it mud free will certainly help. The exhaust does have a little movement in this area and you should be able to prise the rubber from the peg to ensure a good clean.
Bearings can be tricky, but as previously noted - they are definetly worth having a go yourself, or approaching a buddy to give you a hand, as its the garage's labour costs that will kill you.
Good luck with your ownership.

Previous owner of a 1988 BX19 RD & Previous BX Meteor & Xantia Owner.
1995 Toyota Estima Lucida X Diesel