Fix no start issue with my car

Very poor customer service. I had my car towed their because it wouldn't start and had them perform a no start diagnostic which was $89 dollars no problem. The mechanic told me the part is on back order for 4 weeks but luckily landers dodge had the chance only one in town for $300. So my total with parts and labor would be $512.30 out the door still not a problem. Told the mechanic not to perform the work until I contacted them back. Well they took it upon themselves to do the work anyway. Come to find out the part is available everywhere in every parts store in little rock has them for a $89-$110 rain including landers dodge. When I confronted the mechanic he stated that all shops mark up their parts. 125% markup is a RIPOFF. I SPENT $1000 dollars getting my a/c fixed last year with this same shop and this is how you treat a repeat customer by marking up a part 125% I won't be going back to let them change the oil on my lawnmower.