Bottom line is: Research, reasearch, view, view, and build a personal knowledge database as best as you can.
The down side to this is that the "peach" car is viewed, recorded into your knowledge base and eventually bought by somebody else. This is the risk you have to take but the more reviews, viewings etc. you do the greater your knowledge ensuring you skip over the duds and only focus/become interested in the real quality candidate 130s out there.
It has already been mentioned that £4000 is a possible fair going price for a good car. Unless you can find an old granny looking to sell off real gem of a car then look at cars around £3000 +/- £500 as a starting point. Then go and look at £1000 to £2000 examples and unless you find a "granny" model then you should be able to see the vast cavern that has to be bridged by time, money and heart ache to get from the low end to the high end.
Many have fallen in love with the Strada 130TC, jumped in there and then later have had to withdraw because the real reality of owning and running ANY rare Italian classic car is far more than they bargained for.
Running a classic Miget, MG, Spitfire, many classic Ford, Vauxhauls etc is a walk in the park compared to keeping a GOOD 130TC at the top of its family lader.
Having said all this the 130TC is a great car to own, love, enjoy and keep running. You just need to ensure you get a good quality start and are prepared to put some effort and £s into the enterprise.
If you do then there is plenty of experience, knowledge and people out there to help you.