I was going to suggest about 2k as well.
However, you simply must have the Devil Spawn double skinned engine bay chassis rails vigorously inspected. This may mean dropping out the front bumper, but if you drop the plastic tray and get it hoisted, you should see any impending rot issues like “swelling” especially around the ARB mounts. If you see rippling or whatever, they are going back to oxide inside…ready to erupt any old day.
Exact same car, been there, done it.
I’m dreadfully biased, but given it’s silly low miles, I’d agree it’s a goer.
Anyhow, speak to Andrew at Autolink in Dumfries come the day, and tell him Robin in Falkirk referred you. He’s one of our best “trustees”. I don’t kno0w if he does repair panels, but even chassis rail sections are now available, and sills/ rear arch sections always have been.
I definately drop out every single fluid from brakes to coolant ( unless it looks fresh)…and have the calipers & discs inspected.
While you are at it, I’d get all the wishbones cleaned up, Hammerited, and inject Dinitrol or similar inside them. They rot form the inside out. Also clean up the PAS metal piping & treat. They can perforate and trust me, a used rack is a pain in the arrissimo to find at a decent wedge.
In the end, SWMBO having owned it 14 years as a daily, now enjoys it as a retirement companion. To her, like you, it seemed worth it.
105,000 miles, and just loosening up nicely. 
In the end, you’ll have one of ( in my opinion) finest 5’s ever made blessed with what I regard as the best interior in terms of durability, quality and design they ever did.
I do love my Mk1, but it’s an Airfix kit inside by comparison!
things you learn on this forum.