Your budget is quite ok for a fibreglass cruiser.I have a Norman 20 and the costs are roughly,
Mooring £60 pm
Insurance £93 pa
BSS £130 every four years
Canal licence Forgotten how much.
The Norman 20 is a sound design,however the accomodation is very cramped.
You can pick up a Norman 20 very cheaply,but for a really good,fully equipped one (good engine,decent gas cooker,good fit out,good paintwork some form of heating,gas or diesel.) expect to pay £3500 to £4500.
Suggest you visit one or two Norman 20s to see if you are supple enough to move around inside.
There is also Norman 22,23,and 24.These are much roomier boats and they handle pretty much the same,and are fine for single handers (once you have fitted mounting blocks in the cockpit.Because if you are a bit short legged getting in and out can be a bit of a stretch)
The bigger Normans will cost more of course,but again you will see some advertised cheaply.
Suggest you join The Norman Owners Forum (as well as CWF of course) and there like here you will find everything you want to know about Norman boats,as well as (like here) many knowledgeable people willing to share their experience.
Let us know how you are getting on.