I bought a 101x10 enclosed in 2002. Cost was $2300 w/ 10" tires, tongue jack, & spare. I added ski guides, mats, & a tilt shock myself. The trailer is all aluminum & has held up great. It has the little hump for extra head room. Absolutely the best investment made to keep sleds in top shape if you have to trailer. Also in the summer, all the sled stuff goes inside this trailer.
But...now I wish I had a 11 or 12 footer. The newer sleds extend more in the back. My newer IQ just fits with skis all the way up. Also if the windshield is a taller, like a 20" widetrax watch out it will get squished. The sleds sit higher.
I priced a new 12' sledbed with snopro topper. Cost $3600

That was with no mats or guides.
Used enclosed 12' go for about $2k-2500 in my area.
Used enclosed 10' go for about 1400-1800.
If I was going to buy today I try definately get a drive on/off 11 or 12 footer.