I recently managed to go online and travelodge Bham Airport was for only £33, plus £7 parking. I risked it and turned up an hour later and room was still available (10% more for walk-in rate). I was able to pay cash, but, as usual, had to show ID. Access to room was using key cards, so if the girl is not with you, you'd have to come downstairs and meet her (you could always arrange to meet outside in the car park, and then walk in together. Lift are next to the entrance, so no long walk past reception/bar area).
Rate is flexible, depending on occupancy. Another night I checked it was £53.