Hi Treeve,
There's plenty of 'add-on' screw teleconvertors that'll fit on the front of your current Fuji. It's probably the cheapest option...around £100-150 will get you one of the better ones.
If you're wanting something with better image quality, so would prefer not to use an 'add-on' lens with your current camera, don't limit yourself to Olympus or Fuji due to the card compactability....There's adapters available (between £15-30) to fit your selection of xD cards into a CompactFlash sized module. The module can then be used in DSLR's that take CompactFlash.
It's not an ideal solution in terms of process speed (if you want to shoot rapid mode, there can be a delay processing the images)....but it does open up the world of Canon!....with more than one or two Nikons also taking CompactFlash.
Secondhand opens up more possibilties...quite a few of the older DSLR's Canon 300D, Nikon D70, with a 500mm mirror lens for example, should give you plenty of change from £500.
Just some ideas I thought I'd share with you
Good luck hunting
