The plural would be much better but then the plural might command a much higher fee. Try and find out who the buyer is, it may just be initials of a company. gig could also stand for gigantic or for hosting rather than music but there is a gigguide so the singular might work.
It all comes down to personal needs in the end I think and if you look at three letter sales 3k to 5k is a good region but then if the buyer is developing a gig site it could be worth more to them. For instant they could be into security, man management, event management and the three lettes g i g would be amazing for them. Others know better though.
Cheers
Lee