In general, money is a mass noun, so you use it as a singular: no money was required, no government money was used.
Maulik V is correct in noting that there is a difference between money used and money required, by the way. However, I think that is not a problem in this case.
To express the idea that the study did not cost money, you can say it was done for free, but since you want to include the actual costs of €0 that is not an option.
An amount in euro is usually written in the same way as an amount in dollars, by the way, with the amount following the currency sign.
You could try something along the lines of:
A study performed at a cost of €0.
A study at €0 investment
Searching for "X" in "Y": how a €0 investment yields results.
I originally wrote €0.-, but as @Steve Melnikoff noted:
[W]hile using a hyphen to indicate no cents (or no pennies, if we're using pounds) is not uncommon, it's not normally printed like that. So this should appear as "€0.00", or just "€0".