Time Spent Before Making a Purchase

I made a offhand remark on Twitter awhile back but was curious about how much time people spend researching before purchasing something. 

“Amount of time people likely spend researching buying a: car > tv > plane ticket >  crowdfunded startup > stock. My guess it is exponential.”

The irony of course is the volatility and spread of the results is much higher at the right side than the left…

Anyone seen any research or surveys on how much time people spend researching X before buying?

Thanks in advance, will share results…