A camera or device capable of recording 1080p at 25fps. This includes recent models of iPhone, Samsung, Sony Experia and other smartphone devices.
This would also encompass lower end digital cameras and a number of digital stills cameras e.g. Canon PowerShot SX620 HS (RRP approx. £200) or Sony HX300 (RRP approx. £269 and entry-level DSLRs such as the canon EOS220d (RRP approx. £650).
To improve the quality of smartphone filming, there are a number of add-on lenses for common smartphone devices, which can be purchased at a reasonable cost e.g. the Mpow Clip-On 180 Degree Supreme Fisheye Lens (RRP approx. £13.99) or the Motojojo Magnetic iPhone and Android Lens (RRP £20 plus).
The improve the quality of smartphone sound recording, there are a number of add-on microphones for common smartphone devices, which can be purchased at a reasonable cost e.g. the Olympus ME 51S Stereo Microphone (RRP approx. £39.99) or the IK Multimedia iRig Mic Cast External Microphone (RRP approx. £29.99).