crowns after root canals after onlays

i had 2 onlays on 06/29/10 on teeth #19 and #3 because i chose to save my tooth structure and not be cheap. every since the day i had these onlays done i haven't been able to chew on #19 and now #3 is acting up.

went to the dentist yesterday 08/03/10 and he says i need a root canal on #19 and possibly on #3 which of course, means i'll need crowns too which is what i tried to avoid in the first place because i wanted to save the tooth structure!

i am so upset. is this a common practice or am i being scammed?

when everything is all said and done, the grand total would be almost 2000 dollars out of pocket and i have insurance!

i have had 2nd and 3rd opinions and i'm going to my old dentist tomorrow for a 4th and paying him out of pocket for a consultation because i just don't trust this new dentist. i have NEVER had to have any dental work done before besides just fillings. this office also got me for perio scaling and root planing because i had 6,7 and 8 pockets and i have no history of gum disease. please help! thank you