Several potential terrain objects for both fantasy and sci-fi/pulp.
There were two castles, a pirate ship, and a '30s style rocketship, all made of unfinished wood. The castles had arch openings, so didn't look like birdhouses, and the opening in the rocketship was in the right place for a cockpit door or window. The pirate ship did have a round opening in the side, but it was still workable. There were perch posts on the rocket and the pirate ship, but those would be easy to remove or disguise.
The castles would work in 10mm or possibly 15mm as small keeps, towers, gatehouses or shrines. The rocketship was large, but would work well with any scale, depending on how big or important a ship you want it to be. The pirate ship is of course very cartoonish in style— but if you like toyish fantasy (like that duck ship someone else here scratchbuilt), it would fit right in.
I didn't price the things, as I wasn't in the market, but I can't imagine they'd cost much; probably $9.99 USD or less. And of course, Michaels usually has 40% to 50% off coupons readily available online or in the Sunday papers.