Find the game price

store.steampowered.com
gog.com
https://www.humblebundle.com/store
http://www.cheapshark.com/

Check the play time

https://howlongtobeat.com/

Do the math

Price per Hour  = Price/Hours
eg. Stronghold HD 3.99€, 20.5 hours -> 0.19€/hour

Decide if it is worth your money

About short games:

Article regarding game prices
http://www.gamasutra.com/blogs/JoshBycer/20160915/281419/The_Ugly_Truth_of_Game_Prices.php