I've both tendered FEED designs and been involved in building...

I've both tendered FEED designs and been involved in building them. Sibling of mine still works at a firm.
This is fairly typical. Going rate for the eng is typically charged out anywhere between $100-$125.

Project Manager would either be flat charge or a higher rate. Same as senior/principles who review are paid more but less hours involved juniors/mid level do most the grunt work.

Be a full few time people involved in the project start to finish inclusive of the project lead/principle and then a bunch of other people providing various levels of input etc.

Do the math. 12weeks x 5 days a week x 10hr days = 600hrs @ $125p/hr = 75k. Equivalent of 4 and a bit people work full time everyday all day for 3 months on this project. Also, that's the hours on paper. They then would have juniors/mid level doing to grunt work. i.e. more hours being done than reflected juniors paid less than the costed rate. It'd be closer to 6-8 people on the project but only a few full time.

Remembering that whilst the charged rate seems high, typically in their pocket they might get half that. The rest is the companies margin, the various overheads of the business and relevant support staff for the business etc etc.

Irrespective of all that, the fact it's shares is good. Company has vested interest to deliver best outcome and on time and that 300k fee can turn into multiples thereof. Bugger it up or cause delay and your fee goes down.

Spilt milk this conversation but thought i'd weigh in.

SF2TH