First, I would def not go asp, it would only be a choice b/w asp.net and php...
There are def advantages to both. First, asp.net being a true object oriented language, where as(the last I had checked) php was only implementing some parts of OOD. they both have huge developer base, you can go to asp.net forums and see one of the most active forums around. TONS of knowledge there. Second, php works quite well with mysql, which is a decent db, but severly lacking for larger applications, whereas asp.net would link to mssql, which is an extremly robust db. I know you said its just a band site, so php/mysql would be cheaper by far for this type of application. But I know you can find cheap places to host asp.net/mssql also. and there are tons of scripts(some free others cost) in both php/asp.net to get a site going up fast. Finally, php doesnt do alot of postback to the server by itself, you must rely on javascript to do this type of work for you(for immediate results), where as asp.net is an all in one, no need to learn 2 languages...but you can integrate javascript/vbscript into asp.net if needed/wanted.
What language are you programming in currently? I lean towards asp.net b/c that is what I use at work, but I have dont alot of php(4) in the past. php is getting to be more and more like java/c and asp.net can be c# or vb, its totally your choice. So the language itself might make a difference to you if you already are familiar with one or the other.
just my .02$