I would hope "reasonable" means they won't reimburse you for dining at Ruth's Chris every night or for a $100 bottle of wine but normal meals are ok. Likewise for alternative travel: won't reimburse for using NetJets but a $1000 DL fare is ok. If F on another airline is the only option, I'd take a screenshot to prove it.

GSA per diem rates are a starting point, but its rare to get those rates for hotels on your own, especially during holidays or high demand times.