I assume you mean wool ones?
I'm skeptical of this practice where people generically recommend brands over the internet. Clothes fit differently on different people, and if there was one brand that perfectly fit everyone, then they would probably have a monopoly on the market.
That said, for a budget around $50, your only option really (outside of eBay and SF's B&S section) is Mabitex, possibly also Incotex. These can be had at Daffy's for about $50, but go as low as $20 if you're OK with cotton. If you're not on the East Coast, your only hope is to find them on eBay or StyleForum for about double that price. Unfortunately, both brands have short rises, and I believe they've been getting even shorter over the years. If you don't tuck your shirt in, or if you're younger, perhaps this isn't an issue. For me, a short rise is a deal breaker, as I prefer something that sits above the hips.
I know it's outside of your budget, but I would also recommend that you consider options such as Howard Yount. On sale, they can be had for about $150. Consider this - most men on StyleForum, including myself, have something between fifteen and thirty trousers. Most of them don't get worn. Instead of buying fifteen to thirty at $50 a pop, invest in five and make them $150 a piece. I think you'd be much happier.
I have two other sources I like for trousers, but to be frank, am hesitant to reveal them. I don't like competing with people during sale season.