I always look for healthy, if I can bare to spend any hard cash on plants that I could grow from cuttings or seeds! Am so mean when it comes to buying plants, so I do love a bargain!
Most expensive plant I have ever ever bought, and it was my wedding anniversary pressie last year, was a black stemmed bamboo. It only had 6 shoots, but they stood 12 foot tall and it cost 60 quid!! Had a look at it today, and around the base, 16 new shoots coming. Planted to hide the shed, and the way it is growing, it will hide the shed and home a family of pandas! ;D