Matej Vydra or Carlos Fierro. Both far better than Dwight Gayle. I'm also playing in SPFL & both came to me but need to shell out £25k/week wages for Vydra - cost £1.4M
Fierro is usually still @ Chivas (Mexico) and cost me £3.2M on £8k/week wages. Aldo de Nigris, also @ Chivas, is another slightly cheaper - not as good - option.
Oribe Peralta is another quality Mexican (although he'll be 31 in 3rd season), John Guidetti on loan, Lucas Viatri from Boca, Angelo Henriquez (Man U) was on loan @ Olympiakos in my season 2 so you might be able to loan him season 3, Sebastian Tagliabue if you can pry him from Al-Wahda (UAE), Denis Stracqualursi (Coritiba), Wanderley @ Al-Arabi (QAT).
All the above well within £4M and most will leave you with change.