I know this is something that most people hate to do, but we're in business and everyone of us know how hard it is to keep going at certain time.
I've found these templates very useful in my situation: http://freelancember.com/email-templates/
Don't forget that raising your rates means that you'll be able to stay in business for a longer time.
Even if your clients rejects your proposal, it's still worth trying.
What to do with the new money? Start a saving account and use it as your personal insurance for tough times, or invest them in your business to provide even more higher quality.