Well i got mine from oldhamfiatgearboxes on e- bay it cost 415 pounds which is about right if you want one thats been rebuilt properly!.
I found them good honest guys to deal with!.
It was fitted by my local independent garage for £350 which equates to about £100 an hour inc vat! all in-including new fluid around £780. so your prices look very high! .
If you choose a garage to do the work at a reasonable price similar to mine, the gearbox can be delivered direct to the garage of your choice and they can arrange the sending of your old one back to oldhamfiatgearboxes as its a exchange deal! .
It all worked out ok for me and could for you to as doing it this way is half the cost of what you have been quoted!".
Those prices do NOT include a new clutch which i absolutely recommend you do at the same time as its a false economy not to you dont want to be taking it apart again in a years time if it was to fail !- these can also be bought from e-bay for around £50 to £80 ,make sure you get a kit that INCLUDES a new release bearing!
As ever chose your sellers carefully check there feedback ratings and look for a 100% and then dig into that feedback to make sure its been earned as a SELLER as some some 100% and when you look at it, it is only as a buyer with no seller rating at all!( BAD FORM E- BAY!) good luck.