What is the best budget after market cooler I can get?

Cooler Master Hyper 212+. That should fit pretty easily in most modern ATX cases including the Rosewill.

are you absolutely sure?

Yeppers the best budget cooler I know of is the Hyper 212. There are better coolers but I can only find them if you state your budget. Anyways I do recall last black friday or maybe the year before there was a Cooler Master V6 GT on newegg that came to 24.99 after mail in rebate. The v6 gt is better than the hyper 212 and it was priced less than it. My suggestion is to wait till black friday to see if any other coolers go on sale.

Will the hyper 212 fit in my case? I saw in the feedback that apparently it's really large.

Okay, I have a Rosewill Challenger Black Gaming ATX Mid Tower Computer Case. Is that good?

It should fit if your case is the Rosewill Challenger.

Sure I think its a great case for the price. It is after all recommended by Tom's and its also on sale, 33% off so its a steal.

Please try Thermal Right "True Spirit" or "True Spirit 120M".
http://www.thermalright.com/html/products/cpu_cooler/tr...
You can get it from
http://www.nansgaminggear.net/ProductDetails.asp?Produc...

Unfortunately they both just went back up to regular price from the $20 sale price, but I have both the Gaia (120mm fan) and Logi (92mm fan) towers from Xiagmatek. I can't say enough about the quality and would put both ahead of the 212 Evo. However, for $30 and $25 respectively for the two models at the moment, I can see where there is more competition. Your price range of $50-100 is hardly on the low-end for CPU coolers though- you could look at the Noctua NH-C14 for $85, which is only 130mm tall and would fit any case, and is also one of the highest rated in terms of both cooling and sound level regardless of size according to FrostyTech's review. The Xigmatek Aegir is $60 right now, and is (if I recall) the highest rated air cooler on the market right now.