Define affordable. Also need to know how many tools/experience you have available for the work.

Cherry is really a mid range color---not dark at all. Many pieces of furniture labeled Cherry stain are actually birch or some other wood stained very dark and called Cherry stain.

Walnut is dark and stains darker well. Oak takes dark stain well, but has a rough looking surface. Ash is less expensive that either oak or walnut and stains darkly well.

Someone may recommend poplar, the trouble with poplar and stain is that poplar sapwood and heart wood are two distinctly different colors and those differences are not covered by staining.

Maple may be recommended, but it is very hard to get maple to take stain evenly. And dying maple is better than trying to stain it.

All the above are available in plywood---which can lower the total material cost/working time substantially.

Good point about "affordable." I am on a fairly limited budget. I guess it's still a little vague but I'm looking for a type of wood that will look like it belongs in a nice home office without having to spend as much as those upscale offices would. Oak is probably out, since it has the rough looking surface. Sounds like walnut and ash might be good choices, especially if they're available in plywood. Thanks for the advice.

Mahogany is less costly than cherry, walnut or quartersawn oak, and will stain up dark as well as any wood. Plywood and mouldings are available off the shelf at my hardwood dealer as well, but YMMV. IMO, the easy-working characteristics of mahogany place it above maple, cherry and walnut. Each wood left natural has an appearance worthy of use on its own merits. You only run into difficulties trying to stain light woods dark, or trying to get the plywood to match the solids. With walnut and cherry, you will run into the difficulty of lighter sapwood. This will mean living with it, or ripping it into smaller widths to trim the sapwood off. If you live with the sapwood, it can be toned down somewhat, but it requires an extra finishing step or two.
Poplar can be stained dark very well, but for color, not grain. IOW, you will end up with something dark, but it will have an indistinct grain.
Here's my kitchen cabinets in oak, I don't see any rough-looking surface.

I'd suggest plywood as the most economical alternative in terms or yield (lack of waste), stability, and lack of defects. You also know a piece of plywood is 48" x 96" and a saw kerf is 1/8" (depending upon your blade), so you can plan accordingly. Use solid woods for facings and moldings.

After that, there are some woods that stain well and some that don't.

A friend of mine always says something like, "The best way to get something to look like cherry is to start with cherry."

Before committing to any finish schedule, try out a sample or two on some cutoffs.

Poplar is usually the cheapest solid wood. It takes dark stains well and can be made to look like dark stained cherry, but not natural cherry.

Shop grade birch ply is the cheapest stain grade material you could use. Add solid birch facing to hide the ply edges. Birch takes most stain well and can be stained lighter than poplar.

Real cherry ply is over $100 a sheet.

Sometimes I find lower grade S2S or S3S cherry wood at a hardwood wholesale distributor for under $5 a bf. It has way more color and grain variation than clear heart cherry, but the price is right and some people like wood with color and inclusions.

Plywood at $100 a sheet is just over $2 a square foot. (48 sq. ft. in a standard 4x8' sheet). And as I mentioned, you can design around fixed dimensions to reduce waste, for example you are not stuck trying to get 8" wide boards out of a 7" wide and a 5.5" wide board.

Hate to tell you this, Bob, but 4x8=32.