Good morning

"So if I buy a second-hand bike which is old but is of high quality ...."

A few years ago I bought a 531c Ribble with Shimano 600 off ebay for about £120.

After riding it for a few miles I ended up replacing;

Two tyres, £20 each for Gatorskins, or about £12 for Halford's own brand,
One chain ring about £12,
One chain about £10
One cassette about £25

If you don't already have the tools, then it's about another £40 for a chain whip, cassette tool and chain splitter.

Okay I now have some new parts, but the wheels are getting near the end of their life as well.

If you budget for all of these spare parts then you are getting close to a new bike of reasonable quality.

Bye

Ian