I managed to put a full loop together for not much more than your budget:
Barrow Composite A-RGB CPU block: £36 new
Phanteks 2080 Ti Chrome & Plexi block: £65 (eBay)
Job lot of Barrow 13/10 Soft Tube fittings: £50, Members Market
Alphacool 280 & Bykski 240 Rads: £55, Members Market
Barrow D5 65mm Pump/Res Combo: £48 (eBay)
EK Cryofuel Electric Purple concentrate & Mayhem's Ultraclear 13/10 Tubing (about a £20 delivered from OCUK)
Total (ish): £270
Just need to keep an eye out on the MM & eBay for job lots of fittings - not everyone has the time & inclination to list individual bits for sale, so I lucked out with over £300 of virtually new Barrow fittings (all in their original orange packets). That's where the major expense in any loop lies. The money I saved allowed me to splurge on some custom modular cables for my PSU (ShakMods - also brilliant value).
Edit: I appreciate you can't spend a voucher on the Member's Market or eBay, but just showing it can be done, without such huge layout...
