In very, very simplistic terms there are two models : the light pattern and the standard.
The light pattern is just perfect for bell target work, they are slightly shorter overall (but with full length stocks usually), a little lighter and run about 5.5~6 ft/lbs and all are .177 I believe.
The standards are longer overall, heavier and more powerful and come in .177 & .22 flavours
Within this there are all kinds of variations especially in the triggers and stocks with premiums for Lincoln Jeffries models, fitted peep sights, .25 calibre, etc
Decent complete standard ones start at £150 if you're lucky with nice examples fetching over £250.

Others more knowledgeable than I may disagree...