Not a good idea to draw conclusions from an eBay asking price. Most ebay cars go unsold with reserve or opening bid not met.
Not usually realistic to plan on buying any car, paying to have it restored, and making a profit either.
TR3 prices seem to me to have been quite flat since at least 2005. There was one notable exception in 2010 where a 3A went for 60k in Britain. Not sure, but I think that was one of Bill Piggott's exmplar cars for his <span style="font-style: italic"><span style="font-weight: bold">Oiginal TR2,3,3A</span></span> book.
It seems to me that a TR3 would still have to be just about flawless to bring more than 30K.
My .02 (again)
Tom