I think it's very difficult to answer this across different eras in English football. I think most would agree football is completely different now from even 1997 let alone in the 80's and 70's. Back then players and football in general didn't have the same value it does in today's society. Money wasn't there and clubs never saw the worth of their players or the sport as a whole. I think the fairest comparisons is within each era. Breaking it down that way allows for comparative discussion.
His goals weren't that valuable though. All they helped win was CL qualification. Rushies goals won cups and leagues.
Not really Ed,the same trophies are still there to be won so winning trophies is still the modern day equivalent of winning trophies. CL qualification is very important, worth more than a couple of them and you need to qualify to get yourself in a position to win them,but Torres goals didn't lead to that.
If we won the league in 13-14, definitely Suarez. Even still, what a signing it turned out to be from a much maligned league. In terms of both output we got and the profit from the transfer, hard to look past Coutinho, dodgy back and all!
A very important part of analysing money is to compare the prices 20 years ago to the prices now! Especially in this case, when the prices in soccer has far surpassed the increase in money in general terms, like normal day to day life spending.
Worth a mention too - after Euro 96 I remember the Utd fans all laughing and taunting us that they had beaten us to the signing of Karel Poborský, and left us with an alice band wearing pretty boy named Paddy Berger. Similar fees (3.5m to 3.25m), but we got the better end of the deal. 6 years of some glorious highlights, and fantastic hair *interesting fact - Paddys next door neighbour during his Liverpool years? - a certain Sir Kenneth Mathieson Dalglish MBE
https://www.goal.com/en-ie/news/liverpools-15-best-signings-of-all-time/1hkhr0cg72nz719ilkcjl328ov Interesting read on this topic put together by Melissa Reddy. Think a good few have already been touched on here.