It's what does my head in mate, people seem to think '20' goal strikers grow on trees or something, atm in the league it only looks likely that Suarez and Sturridge will get those totals this season, last season 3 had 20+ in Van Persie, Suarez and Bale, the year before that Van Persie, Rooney and Aguero had 20+.
All those have either been sold in the past for a lot more than 20m or would certainly cost 30-50m if they were sold minimum.
Players of Lukaku's age and goalscoring record in a top league are comfortably 15-20m worth of player
Especially when you consider he's missed at least 8 games of a possible 38 this season in the league. We'd have been looking at close to 20 goals from him with a full season of matches.