With a budget of $400 (US?) for new gear, I recommend getting a Blues Junior, and putting the rest into some effects.

If you're willing to go with used equipment, see if you can find a mid-70's Ampeg VT-44. Its a 60 Watt all-tube combo. With its four 10-inch speakers, it actually comes out every bit as loud as a 100+ Watt amp. Jimmy Page is one of my main influences, and I find this amp is a big help toward getting a good Led Zeppelin sound