A bike is only worth what someone will pay for it...
Without seeing it, swingarm Model 7's seem to sell for
£5000 to £6000 in the UK, as a rough guide.
Obviously, condition is everything. http://www.carandclassic.co.uk/car/C250964
That 8" front brake suggests this is more a 1954 version.
Don't know what price this was, or how long ago.
A 1953 model may not have had a chromed tank ex-factory, due to the Korean War.
This lack of sparkle can keep the price down a little compared to other years...
A Model 19S for comparison.http://www.ebay.co.uk/itm/321320993570
No connection with me, etc.
Note that these comments are coming from afar, from Australia,
Although prices and bikes here seem similar.