The Ashdown MAG stiff can be had cheap. 300W and a 4x10" might be overkill for a bit now, but you'll be very pleased you have a slightly more capable rig when you guys move out the garage.
I know you'll do what I (and most others) did, which is to say that you'll think that no one can ever really need that much amp and you'll be just fine with a 15" combo amp with around 100 watts. You're wrong, but we've all been there.

I had a Crate BX80, the standard is one of the Peavey combos. Look for one that's missing some tolex covering, they're the cool ones.
What might be useful is to get yourself some coffee (or some whiskey) and mentally prepare yourself
to read the relevant bits of this. Set aside an afternoon. But it's worth it before spending any of your hard-earned cash. Certainly at least the 'Reality check on amp prices, performance, etc' and the 'How many watts and cabinets do I need to gig with?' bits.
Welcome to TB! Stick around and get involved.