Travelling "around Europe" is very general, where do you want to buy? I know about the Netehrlands, lots of dealers with selection s of all types of bikes , all prices, ages. For example
Wim ter Braake Motoren , then click on " voorraadlijst" and get their inventory of used bikes, picture icon ,prices . Google many more dealers by brand.
Or check out the private sales on the site
Marktplaats.nl - de advertentiesite van Nederland, then to the various brands of bikes. to get an idea of what is available and prices being asked . Both sites in Dutch only .
Buying in Netherlands willl mean you must work the export - plate registration route, may be a bother.
PS this past winter or fall a HUBB contributor jens el aleman located in Germany offered to help anyone with the paperwork and other arrangements for buying a bike in Germany. He even had bikes to sell. See if you can find those posts here on the HUBB ( I tried but not enough time nor luck )