Home DIY

You can get guys who will come and drill a hole into the outside pain if glass then flood the cavity with warm air and "seal" (usually with a sticker) the hole they've created. Its cheap but has some issues:

1. The original problem with the failed seal is not addressed so will fill with condensation again.
   
2. The window will be much less effective at insulating.
   
   

If you avoid the big national companies (Everest etc.) then by shopping around you should be able to get a replacement unit for a pretty reasonable price.