There were plenty of 625 only monochrome sets after the introduction of colour. A colour set in 1967 cost about GBP300, about GBP5000 or $14000 in today's values allowing for inflation and the exchange rate of the time. This would have been an expensive luxury. A monochrome set would have been about 5 times cheaper.
In the UK the BBC is funded via a licence fee levied on all TV users. You may or may not agree with this system but that's what we do here. There was an additional licence fee for colour. Incredibly there is is still a different licence fee for monochrome only with a few thousand still around:
http://www.telegraph.co.uk/news/news...white-TVs.html
While I strongly suspect that most (not all) of these people are breaking the law by using a colour set I also suspect it's a political decision not to pursue them. At some point the numbers will drop to almost zero and the monochrome licence will be abolished.
For comparing prices over time I use this excellent website:
https://www.measuringworth.com/ukcompare/
Common monochrome 625 only sets in the UK included many designs based on the Thorn 1500 chassis and on the Rank Bush-Murphy A774 chassis. Example of a 1500 set on this page:
http://www.golden-agetv.co.uk/equipm...?ProducerID=12