Personally, I feel that 50 f1.8 is a nice lens that does that. But I find it hard to use in many shoots in the event. As 50mm on crop, will more or less only allows head/body shots. Unless you have alot of space inbetween you and the cosplayer. So, I end up using 17-50 f2.8 instead.
I was primary using this lens only for the stage shots, (if you are wondering).... price wise, check out the B&S, I believe it have not fluctuate much of $250-$300.
Please also note that this lens is a "slow" lens in the events hall, you will find yourself bumping ISO to rocket high to freeze a stage movement. But, I rather have a noisy shot than no shot...but that's me..
If it's ground shoots that you are after, I recommend that you consider getting a flash first before a lens. No matter how wide your aperture is, if there isn't enough light, there isn't enough light... You may want to post some images to illustrate what kind of image you want to achieve thou...
*btw despite earlier saying that 50mm may be too tight, I manage to take 1 shot using it, (a combination of 50mm f1.8 + flash)*
You need a good 3-4m away from the cosplayer to get this shot.