As usual - it depends. If you need airline-style dispatch rates, then yes, the Jetprop is about the entry-level airplane. If you can be a bit more flexible, then there are other options, although none of them 'cheap' (not a word normally used in an aviation context anyway).
In Europe, the mix of WX, regulations and the historic aversion to seeing GA as a means of transport rather than a hobby conspire to make it rather difficult to use a personal airplane as a mode of biz transport. There are people who do, but again, the Jetprop or the Meridian (better) or some twin are really what you need. Pretty much anything below that level and it's 'for the kicks, unless you can be very flexible with your time.
Other than that, there are of course the fractionals (NetJets, etc).