I can't recommend anything under $30, but I do have one thing to consider, that I don't think has been mentioned, and a way to exploit junk box parts to get acceptable with a cheaper iron.
First, you should consider the availability of tips. Different tips are desirable for different jobs and eventually you'll need replacements. The iron I got when I tried to go cheap didn't last beyond its first tip because it used a non-standard size and I couldn't find replacements. (IIRC- it was branded Weller, but obviously was non-standard crap offered to hit a price point.)
Second, if you can't stretch to the $65-$100 (depending on model, sale, shopping skills, phase of the moon, etc.) for the better temperature controlled models suggested above, you can make a usable controller from a light dimmer & other electrical parts. Years ago I used a rotery switch dimmer, an electrical outlet, a double wide junction box, an appropriate face plate, and a heavy duty extension cord (for wire & a molded plug) to make a power reducer. Wiring this up allows you to reduce the power of a fixed output iron. Combined with a 40W+, I'd suggest 60W, pencil iron it is quite usable.
Of course, if you don't have the scrap box of electical parts to raid you would spend enough on the dimmer box part, I think you'd be better getting the tempurature controlled iron. Around here, I think the Hakko iron from Fry's is the go to deal, especially if you can wait until it goes on sale. (Seems like that is every 3-4 months.) Good setup, section of alternate & replacement tips right there and many other accessories & solders ready to carry out the door. Since you don't give your location, YMMV. Hopefully you have some sort of electronics dealler.