Levi's 511s. Can easily be found at Levis outlets and places like Winner's, Marshall's, etc. for $20-30. 28x32s are usually on clearance too because no one buys 'em.
If you're lanky, slim-fit can be too baggy looking, so go for skinny cuts. Super skinny(ie. Levis 510) are too tight, unless you're punk or still a teenager.
Unisex cuts are good, they're often slim enough for lanky dudes. Some girls' jeans are entirely passable and have traditional crotch size, but there are tonnes of male jeans out there that are slim/skinny these days that you don't _have_ to go this route.
Cheap Monday have some cheap offerings out there. I just 'debrand' them by taking the patch off the rear as I hate their logo. They aren't the best denim, but the price is comparable to H&M and the quality is much better than H&M. If you wanna spend a bit more, a lot of my friends swear by Naked and Famous, which are cheaper than most other raw/selvedge denim. Nudies are alright, but they aren't worth retail, so I'd only cop if they were clearance/close-out.