I’d suggest handbuilt. I’ve just bought this lot;
Stans Alpha Rims: 700g pair £150 (CRC with £10 off)
Sokin hubs (ebay) : 288g pair £59 (best offer)
24+28 spokes : 364g (DT Rev, 7g each with nipple) £30 (rose bikes)
Total weight: ~1350g +QR’s (48g Ti KCNC, £40)
Total cost: £280
OK it’s over your budget, but you could build Open Pro’s (about £40, 420g each)on the same hubs for <£200, or £160 without the QR’s and still be under 1550g even with shimano QR’s. Or going the other way, there are some even lighter (dati) hubs on ebay, but they’d add more to the cost and crucualy pass the £1/1g threshold I usualy set myself.