Good cheap strikers are hard to find, and finding one that's going to cost you £4 million or less is very difficult. So, if you are looking for a cheap striker who can score goals Id like to introduce Mariano Díaz Mejia. Simply known as Mariano.

22 year old Mariano has a great goal scoring record for Castilla(Read Madrid B). According to Wikipedia he has 27 goals in 37 appearances for Castilla.
When starting a new FM 2016 save, you will discover that he will be available for less than £4million. I recommend signing him for a team in the Sky Bet Championship.
Despite being born in Barcelona, Spain he has been a Dominican Republic international since 2013.
This player was recommended to me by a Scottish guy named Allan.
After Allan recommended him to me I bought him on my new save with Middlesbrough.
He is cheap in buying price and in wages. Max wage for him will be £13k p/w.
On my Middlesbrough save he is earning £7k p/w

His attributes may vary in different saves but he will always have 11 Finishing at the start of every save. His best role is a Trequartista but can also play as an Advanced Forward.
So far in my Middlesbrough save he had played 8 games, scoring 4 goals with 1 assist.

Overall, he is a cheap, consistent striker who will score goals to win games.
In my opinion, if Mariano plays most games in your season, he will always score at least 10 goals.
I haven't had much experience with him yet but hopefully he helps me achieve promotion with Middlesbrough.