where are those good brands with narrow neck that cost <700???

40mm will be real good.

i could only think of ebmm neck and yamaha lower end neck
erm...you'll have trouble finding a neck that narrow anywhere...42mm seems to be the narrowest you can readily find..
G&L legacies have 41.3mm, fender jags have 41mm.
It's hard to get mich narrower than that.