Not sure how helpful this is but I bought a decent 18v drill and ensured I had a range of bits up to about 10mm.
Then I bought the cheapest SDS I could find (£30 for a Titan) and bits as I required them. I've managed without a 110mm core cutter as someone's had one whenever I've required one. It took me a while to buy a 54mm diamond core bit and even longer to buy a 32mm masonry bit.
In my first two years I probably spent around £50 on my drill and bits and now seem to buy another bit every nine months or so.
I was wary of buying too much clobber to start with and end up not using half of it. For example, in my cheap plumber's drill bit set from Screwfix (£18?) I've only used 3 of the 7 pieces in 5 years.
It's so tempting to buy huge amounts of all sorts and not use half of it. Additionally, you're lugging a large amount of dead weight in the van which affects fuel consumption. If you leave it at home until you require it, you can bet your bottom dollar (when you're an hour away) you put it in the van last week. With fewer tools, you'll carry them all, use them all more frequently and have less useless weight.
PS - five years on, my Titan's still working sufficiently. I know there are better drills costing more but I've made better use of that money.
