Less than 100 bucks a pair would make me a bit nervous... you get what you pay for.
Might be good at stopping the car, but may not last as long, or might be made of inferior materials that warp or retain more heat than they should. Cheaper stuff won't have the best design for the cooling vanes, may not be as close a tolerance which may affect rim centering or other fit issues for the wheels, etc.
Look for reviews of parts before you buy... if it looks like a lot of positive reviews, and /or you don't mind the gamble, go ahead and get them!
But I too have been looking around for slotted rotors, but will buy soon from d.zeckhausen based on reviews here, and reviews of the brands he carries. Been looking for a year, so you can imagine how many sites I have been to... and since I am only a novice brake expert (

) I rely more on reviews from other parties than the tech specs I look up (just a little more)
Let us know either way!!
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My name is Steve, but you can call me Cueball.
06 Mag Pearl 300C, California Wood, Adjust. pedals, PGII, Nav and Sound Grp II, HID. 22elite Console cover, FlashPaq, Formula One Pinnacle 35%, Blastin Bob's 5db resonator delete, KW V2's, Hotchkis sways, 3-Piece Intro ID 311 22's with Toyo Proxes4 285/30 and 255/35, Stoptech Sportstop slotted rotors with Centric Posi Quiet pads (Zeckhausen), De-Badged/De-Moulded!!