Scanners are pretty much dime a dozen these days as long as they don't break.
As James pointed out, file size of the scans are a function of the format the scans are saved in, and can easily be remedied either through changing the default file save settings in the scanner interface or using an
alternate scanner application with more features.
PNG file format will probably be the best option to save in as it uses lossless compression by default. If you use
JPEG with any real level of compression, you'll lose the sharpness of text and have artifacts as it uses lossy compression. Text documents probably don't need to be scanned much higher than 100-150dpi unless there's fine print involved, and use
grayscale instead of full color unless you need the color in the documents being scanned.
Using a smartphone camera can be a good option in a pinch as Sol suggested, but it can also be a mixed bag with documents that use smaller point text and although it can correct for perspective, the document's sharpness might be uneven. It sounds like you need a proper document scanner in your office, as well as a good laser printer, given the line of work you're in.
Probably one of the best options for the money right now would be the
Brother DCP-7065DN as this both satisfies your need for a scanner and provides you a laser printer that will help drastically reduce future office printing costs. Normally, I'm not a huge fan of AIOs, but there's something useful to be said of having a laser printer that can act as a stand-alone B&W copier in an office environment. The thing averages around $150 most places (Office Depot has it for
$130 until the 6th), uses a
separate fuse assembly from the toner cartridge making for cheaper toner cartridges and less overall waste, the consumables are reasonably priced, good duty cycle of 10k pages a month, network printer support, document feeder with flatbed scanner, the toner cartridge isn't microchipped (like Samsung does, for example) allowing for cheaper DIY toner refilling (if desired), low-toner indicator can be easily overridden until toner is actually used up, built well enough to last if taken care of, and is cheap enough that if something
does break it won't be heartbreaking and you won't be left with consumables that are unique to only a couple other Brother models as the TN/DR420 and TN450 are pretty much universal parts across their entire laser printer line.