The serial # dates your LP53 to 1957 (probably September, but could be a month either way).
As to value. Here are some older threads which may help.
Thread 1
Thread 2
The information from pennineway.fswo in the above links is all good, he knows his Walthers.
Danny's excellent Vintage Airgun Gallery has a useful Walther section if you want to work out which variant of LP53 you have, if you don't already know. HTH