For what purpose , playin in Band , Small Room, Garage , Bedroom, Gigs in bars , Church, only at home ?
Whats about your Fender Mustang LT25 25W ??? Its not very pedal friendly , you wanna go now for Tubes, I guess ?
You might wanna Test Out a Roland Jazz but they are very cleanish and but not for Metal you said playing also Metal,
or a Bugera Infinium, or a Blackstar , a VoX AC10, maybe a cheap Fender blues junior but they are not so much a pedal plattform but this is also not for Metal and might be not loud enough for small Gigs, but would be in that price range ..
To Buy an Used AMP is risky , you might have a local shop got used Guitar AMPs you can try out, then you might get a used VoX AC15, Fender Hot Rod, Marshall DSL20, when you play Rock and Metal something like a Marshall or an Orange would more for you , I would not blind order an used AMP just online.
Maybe just save some more money and take your time and buy then an AMP you more looking for,
I am savin Money at the moment too, and will go for a Marshall 800 Head
or go out and test used AMP if possible at a local Store...
you might also wanna see what sound you want to achieve, not exactly but the direction of it and buy an AMP from there,
because there is a lot to have very different in sound,
for 600 maybe something like a Blackstar would also fit your needs for Rock and Metal , also when it is not really a pedal plattform.