I'd say get a dob, a tracking platform, a toUcam and start with the moon and the planets. If they still like it after that then they can go up and onwards. If they don't.....wellll....they still have the dob, don't they

Plus they can sell the tracking platform and buy some decent eyepieces.
But if they are really serious then an 8" f5 or faster newt on a HEQ5 with a small cheap refractor for a guidescope and DSLR (an old 300D would be as cheap as chips these days,) with a Webcam would be the way to go. The expense is not minimal but not prohibitive either and they are all items that could be easily disposed of if they lose interest. Plus add in a decent 3x or more barlow and planetary imaging is within reach as well.