To be honest at £1100 it is worth trying a scrapyard, you can google a scrap yard that will source the box for you.
Try this; http://cgi.ebay.co.uk/Fiat-Punto1-8-HGT-5-speed-Gearbox_W0QQitemZ280318339722QQcmdZViewItemQQptZUK_CarsParts_Vehicles_CarParts_SM?hash=item280318339722&_trksid=p3286.c0.m14&_trkparms=72%3A1689%7C66%3A4%7C65%3A12%7C39%3A1%7C240%3A1318
The re-cond option would be a good way forward, first one I have seen listing the HGT gearbox!
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