Poplar makes a good paint-grade wood. A friend of mine rehabbed a Victorian home and found it was cheaper to buy a molding machine and have custom knives made. Now, he is an expert woodworker, but it is still an option.

Here is a link that might be useful: The machine he bought

kmealy is right - custom knives will have to be cut for your moldings. I had one small custom custom router bit cut for me by Bull Sharpening in Oak Park (I'm an expert woodworker, too) ;-) and, about twn years ago, it was a little over $100. For a shaper, there will have to be bigger knives, and of course one for each shape you need.

All this will be included in the price you will be quoted from your millwork supplier. Since you will spread it out over several hundred feet of stock, it may not be too tough to justify.

Take samples to several places and get quotes to compare.