The SIDS inspection is for cessna aircraft made between 1946 to 1986. It is supposed to be implemented into the maintainance manuals as off April 2012.Final dead line is sometime 2014 for the initial inspection (inspections are reccuring). Even if no corrosion is found during the inspection.It is still going to cost a bit. A C150 is going to be cheaper than say a 185 for instance. But old airframes will generally have some corrosion.I believe that any corrosion if found must be removed &/ or treated. The problem is that there are some very cheap cessna's kicking around ATM. (Nothing to do with this thread). A C172 from a aeroclub in mid north NSW which is on the coast with a good amount of time remaning on the engine and fresh paint, sold for about $23 K. That is cheap.But it may turn into a expensive exercise once the SIDS inspection has been carried out. Just sayin, its not personal . Buyers beware. PS- I suspect that the year 1986 was chosen because that was the final year Cessna made 100/200 series aircraft for a long while.( they were worried about being sued in the Yank litigation society that it had become).They started production again 12 years after production ceased in 1986.