Find the game price
store.steampowered.com
gog.com
https://www.humblebundle.com/store
http://www.cheapshark.com/
Check the play time
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