A cost effective way to get a better instrument is by rebuilding a violin or hardanger you may not be happy with. If there is enough wood in the top plate it is possible to rebuild and make a better instrument out of it. Sound example from a rebuild violin (Mp3).

The violin to the right was retuned and revarnished for Aly Bain. The hardingfiddle to the lower right was a repair for father, Knut Buen. The instrument is now used by a player in Heddal in Telemark.

The figure shows the resonance curve to one of Vidar Lande's hardingfiddles before (red) and after (blue) rebuild. The largest difference is around 420Hz between "giss" and "a". It can be heard while playing the  highest fingers on the third string while the instrument is tuned in "h". Some places also the response is a bit weaker, eg. around 1000 Hz making the tone a bit less nasal.

Hear the original sound: Vidars_Barth before rebuild.wav And the rebuild: Vidars_Barth after.wav

You may also buy a good looking but bad sounding instrument and deliver it for improvement of the tone. 

Underneath you see a repair of a fiddle that has been lying out under the snow a whinter after being attempted stolen. The fiddle and the case was completely in pieces as you may see, but the case and hardanger became a nice  instrument again. The ink drawings were luckily intact.

One of Aly Bain's violins.

Re-varnished hardingfele.