While it is always desirable to obtain lodging facilities within the established lodging portion of the per diem rate for the chosen locality, it may not always be possible. In those instances when lodging is not available at the applicable per diem rate, travelers should construct a cost comparison of all associated costs, including round-trip ground transportation, between finding lodging at the applicable per diem rate away from the conference locality and using the actual expense method at the conference locality as prescribed in subpart D of part 301-11 of this chapter.
41 C.F.R. §301-74.6