I think size of the eps file is a bad way to price files either do it like DT and StockXpert a flat fee which will net the illustrator $4 or $2.50 respectfully or iStock how complex the file looks. An eps file or equivalent should sell for more as the buyer can scale it up and can use elements from it.
99% of my illustrations are less than 3 meg, just because the file size is realitively small doesn't mean it took ten minutes to make.
I am not going to bother with an unwieldy upload process and slow sales for $1.
Unfortunately even though BigStock has a similar number of images as DT they can't compare in quality or sales so I am not holding my breath for them to increase their prices it may mean people just upload their rejects their.