Yes, you are being ripped off. Anything with the word Telstra prefixed or appended means that you are getting screwed
It's tough to make a recommendation on which carrier to change over to, because coverage is going to be the biggest deciding factor. ie: Three Mobile is only the cheap if you are using their service within a 3-Mobile Broadband zone (capital cities).
Ask yourself where you are going to use this service, then hit the carriers websites (Virgin, Three, Vodafone, Dodo etc) and use their coverage-checker tool to ensure that you will not be paying roaming charges at the locations you plan to visit.
A good deal can turn into a bad one if you are charged roaming costs instead of the standard rate.