Linus is spot on in the approach, but a few properties are off. It looks like 'AgencyContractId' is your Primary Key, which is unrelated to the output you want to give the user. I think this is what you want (assuming you change your ViewModel to match the data you say you want in your view).
var agencyContracts = _agencyContractsRepository.AgencyContracts
.GroupBy(ac => new
{
ac.AgencyID,
ac.VendorID,
ac.RegionID
})
.Select(ac => new AgencyContractViewModel
{
AgencyId = ac.Key.AgencyID,
VendorId = ac.Key.VendorID,
RegionId = ac.Key.RegionID,
Total = ac.Sum(acs => acs.Amount) + ac.Sum(acs => acs.Fee)
});