Um, not exactly all expenses. Eusebius observed:
Then as if to bring a divine array against this enemy, he convoked a general council, and invited the speedy attendance of bishops from all quarters, in letters expressive of the honorable estimation in which he held them. Nor was this merely the issuing of a bare command but the emperor’s good will contributed much to its being carried into effect: for he allowed some the use of the public means of conveyance, while he afforded to others an ample supply of horses for their transport.
Eusebius of Caesaria. (1890).
The Life of the Blessed Emperor Constantine. In P. Schaff & H. Wace (Eds.), E. C. Richardson (Trans.),
Eusebius: Church History, Life of Constantine the Great, and Oration in Praise of Constantine (Vol. 1, p. 521). New York: Christian Literature Company.
There was no state church in 325. Constantine did not make Christianity the state religion. Theodosius I did that some 60 years later.
If you are referring to the Donation of Constantine, that is a forgery. The land that was 'donated" was far greater than just the land on Vatican Hill. The Papacy wound up controlling a large swath of territory in the central Italian peninsula until the 1870's.
Which body would that be?