From time to time, we like to remind everyone of the FAR limitations on per diem costs. FAR 31.205-46 generally limits the cost of lodging, meals, and incidental expenses cannot exceed on a daily basis the maximum per diem rates in effect at the time of travel as set forth in the Federal Travel Regulations (for contiguous US) or the Joint Travel Regulations (for Alaska, Hawaii, and foreign countries). Where do you find the FTRs or JTRs? The easiest way is to use various online resources.
FTRs: (per diem rates for contiguous 48 states), GSA has a nice user-friendly website for FTRs. Use a map of the US where you can drill down until you find the right location. Alternatively, you can find the information by entering city and state or by zip code.
JTRs: (per diem rates for AK, HI, and foreign travel), refer to DoD's travel website. Its not quite as slick as GSA's but will give you the information nonetheless.
It is important to know that Government contractors are not bound by any of the other regulations found in the FTRs and JTRs. The only thing binding on contractors is the maximum per diem rates.
One cautionary note, travel costs, like any cost, must meet the reasonable test. FAR states that the maximum rates specified in the FTRs and JTRs might not be reasonable when no lodging costs are incurred or for partial travel days (e.g. day of departure and return). Your internal travel policies and procedures should cover these situations.