I know it's probably a time thing for a lot of people. But if you can spare the time, you can get to most areas of the UK pretty cheaply by train or coach. It's certainly cheaper than being out of pocket by several hundred pounds when a courier has lost or broken your instrument and won't pay out.
Treat it as a day out, or maybe even a weekend away .
OK, so I have a YP railcard, but 2 weeks ago I travelled by train to Manchester to deliver a cab, then caught a train to Bristol to collect my new Chapman stick, then caught a train back home, all in a day, all for less than £30.
Maybe meet someone halfway, or split the train/coach fare ?
Virgin were offering London to Edinburgh for £12 each way 2 weeks ago !