What does it cost to replace a chassis?

I suggest you change the car

take it to a repai shop for assessment of work to be done and in order to determine the labor cost

then add the cost of the new chassis

you're lucky if you can find an identical model (2008) or similar one

then add the cost in changing the chassis number in the vehicle registration

not to mention there might be alignment problems, fit-up issues, additional conversion brackets

If it cannot be straightened it would cost more than the vehicle is worth to try to replace a chassis. 

It doesn’t have a chassis.

It has a monocoque crew cabin (a.k.a. unibody) with extended frame rails to the rear. 

Replacing the frame is nothing like as easy as replacing a chassis on those few cars which still have them, such as the classic Land Rover, where all the major vehicle components include the bodywork can be unbolted and reassembled onto a new chassis.

Doing the job properly will need major work to the crew cabin: basically the entire floorpan and sills/castle rails plus the transmission tunnel need to be cut from the existing shell and new parts welded back onto it which include the front and rear frame rails. It’s not the same as replacing just part of individual frame rails after collision damage because if the existing frame rails are that badly corroded then they all are, and you can’t weld new frame rails onto rusty ones. Not unless you want to sell a dangerous bodge which will collapse in even a minor collision. The most serious corrosion is where you cannot see it, on internal webbing to the rails and sills.

Unless you are a very experienced automotive welder with all the tools and skills necessary, your ute is not economically repairable. If you can do it yourself then there’s so much work that any profit means you’ll have been working for peanuts.

You’ll lose less money by selling your ute as it is for spares or repairs, and least money by breaking it yourself to sell all parts and then weighing in the leftover scrap for cash.

Ae you sure it even has a chassis? Most small imported trucks have a unibody.

you mean the frame? it would be too expensive.