Currently available and in stock from electronic retailers, Samson Zoom H2 digital recorders work well for an evening of autorecording. These units accept a line in connection from a Pettersson D240x or other detector and record directly to an onboard flash card in .wav format readable by SonoBat. Samson Zoom H2 units cost about 140 USD with a 1 GB card.
Zoom H2 can be set up to automatically parse incoming signals into date time-stamped separate files. By only saving bat pass events, the standard 1 GB card provides ample capacity for most nights. View this PowerPoint guide for Zoom H2 recording for how to set up and use these units.
Pettersson D240x and a Samson Zoom H2 deployed at a field site.
See also more information on longer term recording solutions and recording and enclosure suggestions.