Not just bass guitar players, bass amp designers too!
He’ll be fine with a little low power combo (20-100W) with a single 8″ speaker, in a sealed or ported box (though cheap ported cabs usually sound better if you stuff the port to stop it doing much). Bigger speakers will go louder and do more lows but won’t be so good at the real tone of the instrument until you get to much bigger budgets.
Bear in mind that it’s a guitar which plays the bass line (and the bass line is a combination of rhythm, melody and harmony – you need some lows for the rhythmic function to work but plenty of midrange tone to fulfil the melodic and harmonic function). It isn’t just the rumbly noise under the other instruments.
See if there’s anything local here: http://basschat.co.uk/forum/20-amps-and-cabs-for-sale/
I’m a fan of the little Peavey and Roland bass practice amps because they just work and sound fine.