I have been quoted over £500 for a Lofrans Kobra motor (1000w) so take the offer up before they up the price. OR you may be able to get your existing motor reconditioned for less than £300 depending on it's existing condition.
Take it to an electric motor reconditioner-might just need some minor work-new brushes etc.Even if its burned out it can be rewound.
Also electric motors are electric motors-if you find a specialist supplier again you may well find one that fits.
In my opinion Lofrans and Vetus charge over the odds!