Bare some things in mind though (you'll find this out soon enough)
Alan is right, pedals -> easy, cheap, does the job.
18 watt:
Expensive (The real Marshall one as well as most of the clones) if you buy a complete amp. Your best bet is likely one of the Ceriatone models, but they don't like installing the power scaling on these amps (which makes it loud, louder than your DR).
Unavailable in SA, there's not many reissues floating around I don't think.
You can build it yourself if you have patience and confidence in your technical abilities, not everyone is keen on that sort of thing.
This thread shows how mine went.
http://www.guitarforum.co.za/amps-speakers-and-valves/one-small-step-at-a-time-or-my-18-watt-marshall-build/
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