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Without more information, it is difficult to assess the possible value. A 1.8 engined 160 will usually be more desirable than either a Td or a 1.4 engined 105 and will therefore command a premium in value. The 105 will also probably have a greater desirability and value than the Td - there were only 24 Express 105s in total, and only four were Mk2s. Colour also makes a slight difference with the more exciting blues reds and yellows being more desirable than the silver and greys which made up the biggest part of the Express production.
Ultimately, the biggest effect on value will be mileage and condition.
Over the last couple of years I have seen selling values on eBay and Gumtree ranging from the low hundreds of pounds for high mileage workworn/tatty diesels to £1500 to £2000 for well looked after and excellent condition 160s with a full service history.
These vehicles are getting old now, but have not yet reached proper 'classic' status and MG and Rover values generally are about rock bottom. A good condition Mk2 Express (there were only about 50 Mk2 Express built) will rise in value in the future I feel sure, so (if you have a dry garage or shed) I would strongly consider storing it properly, rather than sell it on in a hurry