This EFI testers dont come up to often, great for 82 MK2s and MK1s I would say a fair price is $80-100?
USED TOYOTA Factory EFI ELECTRONIC FUEL INJECTION TESTER 09991-00100-C
1979 Mk1 Owners Manual Near Mint eBay
Given the age and overall condition I would offer $20 + shipping...
Haven't seen an '79 owners manual in quite a while!!