What have you got to lose?? Do it at least for the experience. If you find you expereince problems doing it, well then you have learnt something new and you will find a way to get round it for the next time.
Also, If you do the job and even if it takes a lot longer than you thought, it might lead onto more work, If you turn it down, it is unlikely.
If you are pessimistic you will stand still or go backwards, especially in these times, but if you are optimistic you will go forward!