seriously. try to find a rivera knucklehead...i have it and i know it can do what you want.
channel one is the marshall type channel..... and channel 2 is the fender type channel. like i said. you'll have to mess with your gain settings when you switch styles, but you can have the sounds you're looking for in one amp. use channel one as your clean channel for the SRV type sound and channel 2 as your dirty. use channel 2 for your clean and channel one for your lead when your doing your satriani type sound.
both channels also have boosts, so you really have 4 levels of distortion.
they go for about 400 to 600 bucks for the head on ebay. i think the 55 watt ones would probably go for cheaper and are plenty loud for a band practice.
i realise it's a bit more than you want to spend when you consider the cost of a cab, but it's definitely worth looking into....definitely cheaper than buying 2 amps.
and if you already have a cab, then it's about what you intended to spend in the first place.