Hi folks, if the reason to shoot the nature is for calendar with dimension 30 x 40 cm. what kind of camera you will choose (the budget is around $4000):
1. Some kind DSLR (Nikon, Canon, Olympus, Sony)
2. Large Format with 90mm
3. Hasselblad 501CM (503) with wide lens 40mm
or maybe something other…
The quality and accurate color fidelity is most important and the calendar will be printed on high quality offset print machine.
The budget of $4000 is only for camera body and one wide lens for the beginning. They could be used.
I am not sure how you can really isolate the camera cost from the rest of the question, but...
If you intend to buy you gear, considering your budget, I would go for a Sony A900 and stitch 6 images (2 rows of 3). On a Precision 360 or RRS spherical pano head... IF you are familiar with stitching and are OK with digital. This advise is coming from me stitching a lot and considering the total cost/time of the shooting.
If the subject is not suitable for stitching, then 4x5 is probably the cheapest approach if you are an efficient shooter than can shoot little but well. Don't forget to factor in the film and scanning costs though.
I would also consider rental as an option if the shooting locales are suitable.