You can't technically charge for use of a repeater, only for the upkeep and operation costs.
You can not in any way profit from a GMRS repeater.
I do not charge anybody and the reason is simple. The moment people start contributing they want a say in how its run.
I do this as a hobby and have substantial investment, its a labor of love. My payback is hearing people use and enjoy it.
Below is the FCC part 95 sub part that outlines this better.
(1) The station to be shared must be individually owned by the licensee, jointly owned by the participants and the licensee, leased individually by the licensee, or leased jointly by the participants and the licensee. (2) The licensee must maintain access to and control over all stations authorized under its license. (3) A station may be shared only: (i) Without charge; (ii) On a non-profit basis, with contributions to capital and operating expenses including the cost of mobile stations and paging receivers prorated equitably among all participants; or (iii) On a reciprocal basis, i.e., use of one licensee’s stations for the use of another licensee’s stations without charge for either capital or operating expenses. (4) All sharing arrangements must be conducted in accordance with a written agreement to be kept as part of the station records