Repair or replace

 I suppose you must first decide how long you are intending to keep the caravan since if it costs £500 or more extra it is money that you are unlikely to recoup in any sale. 

If the fitter says you need to replace all 3 of those items, it suggests to me that he doesn't really have any idea  what the fault is!   You could well spend that money only to find that the basic problem is with the cooling matrix, which for all intents and purposes is unrepairable, and certainly uneconomic to replace.

Possibly the 230 volt element went a while back and the OP has been running on gas for a while?

It would be very unusual that all those items need replacing.

can you not eliminate some by testing first on gas only to see if that works. Then on 240v only.

both of these settings should after a few hours use be checked by the exhaust outlet on upper vent outside van, which should be quite warm on either setting,pherhaps slightly warmer on gas than 240v.

if both these settings create a warm outlet vent,then get the thermostat checked.

it does sound as if you have been advised without proper checks having taken place.

The 12v & 240v elements can be checked by resistance readings after gaining access to the top of fridge.

Maybe two sensible options: but first decide how long you will keep this 'van.

Try a local caravan breaker for a replacement. I got one for £40, lasted two years on electric only.

Buy a cheap electic cool box at Aldi/Lidl/Go Oudoors. Then remove fridge and fit a useful shelf!

While my caravan continues to be watertight I have decided to keep going since I am scared of all the horror stories with so many new  vans!  I was told 20 years for van life mine is halfway there and may well see me out.

I have been told by someone I trust that a new fridge could be up to 1,000 pounds and getting a replacement fridge that is the correct size may not be as easy as you would think, Sizes do vary from model to model. I would let another repairer have a look at it and his opinion may be different. What you have been told seems rather odd. Why gas parts and also mains electrical parts? Hmmm

Dakota,  Based on the age of your  van and the likelihood of not recouping the money spent in either replacing or repairing the fridge.  The advice given by Wallacebob would be IMO be most relevant.  

K