where to put the preposition

[Tukanja]

Which of these sentences are correct?

What I shoud have paid a little money last year for now it costs a fortune.
What I should have paid a little money for last year now it costs a fortune.
For what I should have paid a little money last year now it costs a fortune.

Thanks

[fastforward]

Hello.
Q:Which of these sentences are correct?
I think the second last is correct one according to the grammar.

[Tukanja]

What about this word order?

What I should have last year paid a little money for, now it costs a fortune.

[ETutor]

Tukanja,

I would change all the above sentences to one of these below:

What would have cost me just a little money last year now costs a fortune.

I should have bought it last year for just a little money. Today it will cost me a fortune!

I hope this helps!

[Tukanja]

What would have cost me just a little money last year now costs a fortune.

Thanks

Furthermore the answer's led me to the next sentence below

What would last year cost me just a little money now costs a fortune.

Would someone let me know what does he suggest about putting the adverb of time between the modal and the participle so as to avoid using the past participle have cost but having the same meaning.