Any of the 500's(older I know but meets your budget), 550's (2.5 up to about 1992 or so, go up after that) and the CJ.
All the Citations except for the XL, 650's(III,VII) and 750's (X) are pretty much the same....simple to operate, basically a Bonanza or Baron(I know, not Cessna, but they fly better than a 310!!) with blowers. Technically they are a jet, but with the straight wings it is hard for even a novice to screw up. I see some 550 drivers do things that would kill you in a swept wing airplane, but the airplane is so forgiving that they keep motoring along oblivious to their "jet fopah"
The 550 is the easiest jet I have ever flown(maybe even the easiest twin), and the 525 is basically the same except a T Tail. Single pilot ops is no sweat, the 550's require the waiver, but that is mostly just a formality if you have the experience(insurance drives the SP market). Many of the systems are interchangable and the instrument panels are very close to each other. About the only changes you will see up front between 500's, 550's, 560's and the 525's is avionics and glass, and if they are Thrust reverser equipped or not. (525's do not have TR's, just attenuators.
The 500 type covers the 500's, 550's(all series) the 560's (except the XL) The 525 type covers CJ,CJ1,CJ2 and as far as I know the CJ3 is included.
SP ops are good for the sp varients of the 500's and the sp version of the 550 (you take a weight penalty to be certified sp) All the rest of the 550's and 560's (except the XL) can be flown single pilot with a waiver that must be renewed once every 12 months. No weight penalty if you have the waiver as opposed to the "SP 550"
The 525's have an SP and two pilot type rating availible, depending on the ride you take. Point is, with the SP type rating on the 525 you do away with the waiver that is required for the 550's
The Cj basically replaced the Citation I, the CJ2 replaces the Citation II's and varients(Bravo etc), and the CJ3 (way out of your price range of 2.5) will replace the 560's (Ultra,encore etc.)
There you go....clear as mud, It is tough to keep up with the Citations, there are so many. You have to just about carry a note pad around to know what versions you are legal to fly on what type rating!! I think all the info I gave you is correct but I'm sure that I left a varient or two out since there are so many.
All in All though, it is a good airplane, with a good useful load, not the fastest thing out there but it will get in almost anywhere that a King air will, and the later model 550's and 560's are only 50 to 70 knots slower than most of their swept wing counterparts.(mach .67 and .70) Not much of a difference over the range of the plane. Most of the 550's and 560's will get you 1200 to 1700 nm on a tank of fuel with reserves.
