Quoted £200 for Fob duplicate. Is that normal?

If you just want to add a single new FOB and your system isn't maxxed out at number of FOBS yet, there's a way to program that FOB by entering commands into the car using door locks and other components. Just google "Chicken Dance PriusChat"

However if your FOB is not new or you no longer have an existing FOB to match a new one up you can DIY it by buying a Mini-VCI dongle and install Toyota Techstream on an old Windows computer and then use this service to wipe and re-seed all your FOBS to the car: Lexus, Scion, Toyota PASSCode Calculator / Generator: Calculate Pass-code by Seed number | Immobilizer Pincode Calculator

 

The quoted price is within range. If you have a "fully functioning" key to work from, you could try to program the replacement yourself.

Doing a search here uncovered numerous threads for the DIY process, try this thread first : How to Program a New Key Fob for Full SKS Functionality | PriusChat

Perhaps this thread is more your speed : Finally! How to program a non-SKS key/fob. Detailed! | PriusChat

 

Your dealer is FOS. Ace Hardware can also do them.

Automotive Keys - Ace Hardware

I see you're in the UK which means you probably don't have an Ace Hardware. Nonetheless, it means that Toyota dealers are not the only place it can be done.

 

Never knew this was a viable option, even with the fairly high end keys pictured on that page, I am still having some doubts.

Have you (or anyone known) ever used the FOB programming services being offered by ACE before?

 

Yes I have. My Accord has some weirdo double sided key that's hard to cut and the Ace machine couldn't pull it off. Luckily I didn't really need the physical key. I just needed a new fob programmed. It's just a machine they plug into the OBDII port. There's a process they follow to program the FOB and viola, new fob works.