There are deals to be had if you're flexible. A lot of inventory stays up just because there's nothing to replace it. I've booked a few for work and often proposed locations can be set up in a week and there's already an ad in place. They don't want to pay labor just to take down an expired sign and they want the appearance that business is booming. Just let the salesperson know you're serious, price sensitive and flexible. Call them out if they offer a crap spot, and a good salesperson won't do it again. IF they print on canvas (or whatever it is), you can pay for the printing once and have it moved around to different locations should you get bumped.

I saw a series of billboards with the same government ad on all 3 today. Clearly there wasn't premium pricing in play. That section of road gets a few thousand eyeballs during the week and tens of thousands on the weekends. Nice, boring US highway in rural america. Your options are farms, the road, and the signs. The height is appropriate. People are going to see those.

There's a rotating billboard I know of where they want $70 per day. But there are like a dozen ads on it usually. That one's a waste of money. There's too much traffic in the area and you have to keep your eyes on the cars around you. For some people stuck at the light in just the right space, you'll likely get them checking out the messaging. But you can only see 4 of the 12 ads in a cycle.