I tend to disagree.
I was interested to buy a diesel corolla about a month back (not any more) and during my search I found that 03-04 corolla diesel were for around 6-7 lacs depending upon condition.
Rule of thumb quoted to me by a dealer was that a diesel corolla is priced at 125-150K less than its competitor in petrol/cng. Reason was that, it costs 100K on conversion while a converted one has a market of 25-50K less than its original competitor.
experts on the forum to put me right if I have been guided wrongly.