Unless you have a host that purposely goes down on a schedule, that's impossible to answer. All hosts have problems, though.
No host should go down every single month, so it's hard to put an average on anything.
I think I'd avoid a host that advertised an amount of downtime to expect. It would sound like they're not trying hard enough to avoid it.
Anywhere up to $97, if you use a promo code that many of us have in our sigs. DH gives you $97 referral fees, which you can turn around and pass onto new customers. You can do the same when you join--or you can just refer people and keep the fee.
It's all done through shell access, which is available on all plans.
Save up to $96 at Dreamhost with 96DOLLARSOFF promo code (I get $1).
Or save $97 with TAKESEILERSCASH.