I've never heard anyone say anything bad about the Vox Valvetronix, and from memory, the 50W AD50VT has an upgraded speaker too.
Here's a video demo of the XL (high-gain) version stratrat is talking about
:
YouTube - video review vox valvetronix advt-xl amp rob math
I actually like the
normal one better, even for metal:
Vox Valvetronix AD30VT | Gearwire
YouTube - Vox AD50VT US HiGain
Sersly, at your
price-range you might be better off looking for something like the Vox, or even a Line 6, Bugera (which is real valve), etc. Nothing wrong with wanting a classic Marshall half-stack, but you'd be looking at I think 3-4 times what you want to pay. People want the good models, so even old beaten-up ones are similar in price to brand new ones (check e-bay).
Here's what I think you were after. Hold your breath before looking at the price, and remember, this is just the head, no speakers:
Buy Marshall Vintage Modern 2466 Tube Amp Head online at Musician's Friend