Personally I never trust anyone offering me half price work so unless you really trust this guy, Id say for peace of mind keep your 300$ ( use it to buy good jack and axle stands )and do it yourself, its a pretty easy job and if you think you can do it, you can..just unbolt the dump from the back of the turbo, I found these much easier to do than the 3 bolts joining the front pipe to the dump pipe as these you will find are rusted in hard..
But...
while the manifold/turbo studs should be fine, its the studs at the manifold/engine that crack mostly mate, usually 2 or 3 at either end..i had to replace 5 which also means removing the exhaust manifold which is easy enough ,but drilling out broken studs and replacing them is a prick of a job for a non professional without the proper tools, I didnt even attempt it..You will be lucky if none of them are broken and i would definately be checking this while your in there. I got charged 120$ to do this alone but its a cheap price for peace of mind...plus then you will need a new gasket, 30$ on ebay or 100$ from nissan, i got one on ebay and its doin fine..