Best strike rates in Europe (selected):
1. Mitroglou (Olympiacos) Age 25, 14 goals in 10 matches
2. Suarez (Liverpool) Age 26, 14 in 10
3. Lascak (Rosport) Age 19, 17 in 13
4. Ronaldo (Madrid) Age 28, 17 in 14
5. Kolyaev (Levadia II) Age 24, 24 in 20
6. Luvannor (Sheriff) Age 23 *Defender* 18 in 15
11. Montero (Sporting) Age 26, 13 in 12
13. Finnbogason (Heerenveen) Age 24, 14 in 13
23. Costa (Athletico Madrid) Age 25, 15 in 15
Maybe worth asking Mirallas for his opinion on Mitroglou? He has three goals and an assist in five CL games and his international record is 8 in 28. Transfermarkt (not the most reliable source) rate him at £6.3m and claim that Liverpool have been interested.
Fredy Montero is on loan at Sporting from Seattle Sounders, so there might be an opportunity to nip in for him.
Finnbogason might be an option but it seems like Costa declined to join Liverpool even though they met his 25m euro release clause and he's doing very well in La Liga.