This is the thing though Bob. We only pay £18m if we stay up, at which point (you would hope) Archer will have played a part in securing a further £120m+ of income for the club. At that point £18m is a sound investment.
I don't disagree that Archer seems expensive at £18m but equally these are the other PL signings with a similar profile to Archer
Brentford: Kevin Schade (21, £22m). Scored 5 goals in 32 Bundesliga appearances (8 starts) and has yet to score in 20 PL games (8 starts).
Brighton: João Pedro (21, £30m). Has 4 PL goals (inc 1 penalty) in 31 appearances (16 starts)
Burnley: Zeki Amdouni (22, £16m). Scored 24 goals in 66 Swiss top flight appearances (53 starts) and 7 in 11 UEFA Conference League games (8 starts)
Everton: Chermiti (CF, 19, £10m). Scored 3 goals in 16 Liga Portugal appearances (9 starts)
Spurs: Alejo Véliz (CF, 19, £13m). Scored 17 goals in 53 Argentinian top flight appearances (42 starts)
United: Cameron Archer (CF, 21, £18m). Scored 18 goals in 40 Championship appearances (35 starts). No goals in 10 PL appearances (0 starts, total of 72 minutes)
At £18m, Archer sits exactly where you would expect in relation to those.