JMM

Hi I've recently been playing a few gigs and am looking to buy a decent amp, but I'm a bit unsure as to what to go for. The only amp I've been using for the last 7 years has been a Roland Cube 30. I love the tone of it however I'm now at the point where I need to purchase something more powerful as we'd prefer to start using amps instead of a PA for our gigs. The guitarist in my band has decided to buy a Fender amp that's rated at 40 watts, however it's a valve amp and so we've been told it's on par with a 200 watt solid state amp. I'm hoping for something that can produce a similar quality sound and the same volumes. Is it worth going for a new or second hand amp? After looking through the for sale section, there seems to be some fairly big savings to be had but I'm not sure on how long an amp can last and whether it's worth paying the extra to get a new one? Also what makes are good to go for and which should I avoid? I do like the idea of getting a valve amp (and am just looking through the stickied thread). How do I tell when an amp has valves? I've seen some mention valve preamps but am unsure whether that means it's a full valve amp? I'm currently playing an Ibanez active 5 string and our music is sort of rock/indie if that makes a difference to amp choice. I'm also looking to spend under £500. Thanks in advance