This looks interesting. Only 20 bucks.
http://www.jameco.com/z/MLP105-MadLab-MadLab-Electronic-Kit-Junior-Theremin_2251840.html?trk_msg=L0KPLT7ONMU4R2S0L7ACLCU6EC&trk_contact=UGDGL4H5SDFLKRN285MA7QH42G&trk_sid=CVI4UDK54F3DBDM6FQC8UMT8DG&espm=F49A29A8BDF84DBC8B80A9D4CAB3C673&espc=920A1BF4E3255A5F6EE2416CA3EA2414&utm_source=Listrak&utm_medium=Email&utm_term=Order+Your+Kit+Today&utm_campaign=FREQPROJ&utm_content=FREQPROJ