Firstly because I know Perl (a bit at least, and I really don't want to use ASP), and have used MySQL before for other stuff. It is the cheapest option.
That's not much of an argument, is it? Sure, you don't pay license fees for Perl nor for MySQL. But you don't pay license fees for Java, C or Python either. Nor for Postgres. Note, I am not advocating you should use any of those. But "I have used X and Y, and I don't want to use Z" doesn't make X and Y the cheapest solutions. Development, maintenance, modifications all take time - and people working on them will want to get paid for it. However, I wasn't argueing price.
I don't think the client can afford a dedicated server at all. That basically leaves an ISP.
Interesting. You don't even know whether the client can afford a dedicated server, yet you conclude using an ISP is the best option? Sorry to say, but that doesn't sound like you've done much of an investigation. However, there's nothing wrong with using an ISP. But it is wrong to tell your client his best option is to use an ISP that doesn't give you much freedom. If you can't even install modules of your choice, your client is much better off with an ISP that does give your client at least that.
I don't think that the posting of a job on a jobsite is the kind of data that warrants using Oracle etc.
Did you ask your client how important they think the data is? Can they afford losing the respect of their customers (the people using the website)? If your client doesn't care about losing the data (resumes, etc), then why are they collecting it in the first place? Is your client planning to make money (directly, or indirectly) with said data?
I would appreciate it if you can give me concrete reasons why Perl and MySQL would not be a good solution, even if it is hosted on an ISP.
I didn't say I objected to using Perl. There might be reasons not to use Perl, but your article didn't say (if the application is going to be developed and maintained by a team of 40 Java jocks with no Perl experience, Perl is likely not to be a good choice). I did, however, post a link to a page giving a multitude of reasons not to use MySQL. If those aren't concrete, what reasons are?