W30 Transmission Problems

Hi, I have a 2003 W30 with a major transmission problem and seeking help on fixing the issue if possible!
I love the car but not sure what can be done.
Last time it drove, the transmission got stuck in between gears and it was a pain just to get it in neutral. Apparently this is a common problem with semiautos. It hasn't driven since. A few mechanics had a look but either weren't able to diagnose properly or have told me the best solution is to do a transmission conversion to manual. Have been contemplating taking it into Toyota but afraid the cost would be more than its worth. 

Has anyone had this problem or know what can be done?
I'm in Perth, WA, if anyone has local recommendations. 
Thanks.