Welcome to the forum Daviki,
I agree - if you're fortunate enough to find a well-cared for unit - buying used, 2-3 yrs old, is wise for all of the reasons you mentioned.
We have a 2010 Laredo 265RL, and love it! We've owned both lower & higher priced, larger & smaller, and also by other manufacturers... this is our 2nd Keystone. The 265RL is very similar in size to the 25RK you mentioned: less than 30 ft over-all length, with 1 slide-out; the bedroom/bath area is the same in both units. There's only 2 of us also & we're very pleased with the size.
We have the same 6' 6" truck bed length, and purchased a (manual) slider hitch with our first 5th wheel. Although we've never "needed" to use the slider, we're glad we have it... just in case! Generally speaking, the added cost of a basic slider hitch (vs a non-slider) is usually cheaper than the cost of repairing damages to your truck!
The PDI checklist is a great tool whether buying new or used. If buying used, the (original) tires would be also be something to consider. If the 25RK you mentioned was built in late 2005/early 2006, it's possible that the tires could already be 5 yrs old.
As far as trailer price is concerned - in addition to the NADA values, do a Google search for "Keystone Laredo 25RK". There's a few shown on dealer lots across the U.S. & although those may not give a true price comparison for buying from an individual, the ads have photos which (at the very least) would be helpful for comparing the model. I couldn't find a 2006 brochure, but here's the 2007 (dated May 2006), which may be helpful too.
http://media.rvusa.com/library/07_Laredo_FW.pdf
Good luck with your search,
Terri, the co-pilot [& DH Kevin]