I have purchased an "Economy Windows Hosting with Plesk" account. With this account I can only use POP3 email.
What is the easiest/cheapest way for me to upgrade to an account with IMAP email?
The free Workspace email addresses provided with shared hosting plans are all POP based plans with no upgrade path to IMAP. If you require an IMAP based email address, you'll want to consider one of our other email options that can be separately purchased.
Seems like kind of a ripoff to charge for e-mail. Hostmonster gives you unlimited accounts for free (IMAP or POP). Is there any benefit to staying with GoDaddy if that is the case?
Doesn't seem to be any benefit. You are the mercy of the domain registrar. I have attempted to have go-daddy email pushed to outlook put the POP server is an issue. Cannot even forward email without purchasing an additional go-daddy email account.