I own the WM HighLite (850 fill power high quality down - only 16oz in regular length).
It is generally accepted that WM conservatively rates their bags by ~5deg F, so the WM HighLite bag is "really" a 35deg F bag.
The WM HIghLite bag's fabric is very delicate & requires care to avoid damage. The bag's zipper has operated fine with no fabric "snags" in my experience.
With a poss'mDown sweater and a windshell (in addition to normal clothing), 25deg F is "do-able" in my experience & I consider myself a "cold sleeper" - even at home, indoors, I like to wear socks to bed for ~8-9 mos. of the year.
My sleep pad is a 3.7oz GossamerGear NightLight Torso pad & my pack with remaning gear in it is under my legs & feet.
On cold nights, most of the night, I wear a cold weather fleece balaclava during winter when sleeping.
I sleep in an ID eVENT Unishelter bivy in cold/cool weather, so there is not much air mass to heat up.
Price might be a bit above your stated max however, but it's worth every penny? [not sure of the "Down-Under" price.]
Nunatak makes bags similar to WM, but with more choice & they make to order so custom bags are NOT a problem - more choice of outer fabrics too, from lightweight fabrics similar to that used in WM bags, several Pertex fabrics [including Quantum], to Epic fabric.
Nunatak may be more expensive however - but appear to be well worth it - didn't know about them last year when I purchased the WM Highlite, or I might have purchased a Nunatak bag. Either seems, to me, to be a good choice.
Hope this info helps.