The definitive OTP ( Off-The-Peg ) List (<£500 and <£1,000 sections)

1500 - 1600g is going to be the average weight for a cheap alu frame. That is why is will always be expensive to get to 6.5kg. Average weight of mid range components are around the following and that gives you 6.7kg. Going lighter on any of the below gets expensive.
Frame 1.5
Fork 0.5
Wheels 1.8
Cranks/bb 0.8
Bar/stem 0.5
Seat/post 0.4
Chain 0.3
Pedals 0.3
Tyres/tub 0.6

This^ illustrates why people are willing to pay for items which give very little performance benefit, like lighter seatposts.

The best thing to do would be to drop 300g off the wheelset.
something like IRD cadence, laced 32 3x (rear), 28 (radial, 1x or whatever) front. with CX-rays to some lightweight hubs.

390x2 + 260 + 500 = 1.5 Kg*

(*cant be bothered to calculate nips and tape)