Maybe compromise with maple door and window trim and a less expensive base board. Wishihadthat.com has some very attractive choices in poly moulding which I have found very easy to install and it can take water from a mop or spill without turning into oatmeal.

MDF is a very poor substitute. It is a laminate (paper photograph) glued to cardboard. As soon as you nail it, the nail shows. As soon as you scratch off the photo, you see cardboard underneath. They sag and stretch and there is no way to 'fix' one that is lightly damaged.

If you find the trim too expensive, try moving to a smaller profile. Maple is an expensive wood that is highly sought after. If you purchase MDF trim now, you will have to replace them in 5-7 years because they look pretty bad next to the real thing. You will add even more expense to your project at a later date.

I agree with @Al and @Cancork. Are you painting or staining? Soft maple would be less expensive than hard maple, although it is somewhat softer. Birch is also a good substitute. If you want to paint, poplar is inexpensive and takes paint well.

I forgot one thing-if you go with a smaller, square base now, you can always add a base cap to make it taller later.

I've done a couple of rental houses with MDF casings and baseboards only because the selection was more extensive and the price was cheap. Fast forward a few years later, and I wish I had at least used pine. MDF is easy to work with and looks great at the beginning, but it doesn't hold up well to nicks or bumps and is terrible if any water gets near it. If you are looking for quality and longevity for a house you love and will have for many years, skip the MDF.

Thank you everyone for your wonderful suggestions! I think we will bite the bullet and go with maple, it may be more expensive now but it will be less expensive in the long run.