On the path to essential we all take a few detours to learn things.. one of my favorite 'sayings'.
Scan Tailor fits your original description and price range.
There is a GitHub site for downloading the installer, works on Windows 7 for me, but I see no limitations to prevent it from working on OSX or Linux.
The documentation isn't great, but the software is very good, quite on par with most of the BookDrive or BookScanner types of programs.
Digital Book Collecting, or Scanning or Ripping depending on how you prefer to call the process; is basically two things:
2. Post processing
Capture is usually to a series of TIFF files, which are lossless compressed images files, sometimes people compile those direct into PDF files, but are usually not satisfied with the size or the results.
So the "gold standard" is direct to TIFF (although direct to large JPG is kind of becoming common)
You generally want to make sure the images are scanned at around 300x300 dpi, to make really good Optical Character Recognition (OCR) is possible. (Abby Fine reader has been the gold standard for OCR for years). Also an image is not indexable or "Searchable" which is what people start wanting when they need to search a document.
A PDF will hold multiple TIFF images and the results of an OCR scan in a single PDF file, and its a nice format in which you open and can use the built-in "Find" to skim the index and take you right to a page.
A PDF can also have a full functional Contents page and Index with clickable "hot links" to take you direct to a page.. this is also almost "expected" these days, but first you need software to OCR and index it, and usually someone to make the links for you.
A "Cross Document" searcher like FileCenter by Lucion will even index multiple PDF files in a catalog and let you search between them for references. FileCenter will also work direct with Fujitsu TWAIN scanners to let you capture and OCR everything that will fit in the scanner into arbitrary folders on your computer or home nas device.. its fairly inexpensive paperless office software (and it actually works, I use it a lot). http://www.lucion.com/
For Step #1 Capture you need some type of stable camera stand and a camera to snap a picture of a document/book, if it is a loose group of pages a Scanner can work, Fujitsu usually makes the best and still support TWAIN on their high end. They have Automatic Document Feeders (ADF) and flatbed models, and ADF+Flatbed all in ones. Fopydo makes some stiff plastic construction board type stands for very low cost that will support a book or documents and your cell phone for capturing images, and they are available on Amazon. Atiz makes very high end scanning "booths" which support professional DSLRs and flood lights to illumninate opposing sides of a 'V' shaped cradle with a plexiglass levitated platform for pressing the pages of a book flat before photography. They are somewhat combersome to use and require a permenant location dedicated to scanning. Atiz also former made a Canon Powershot model to take advantage of lesser expensive prosumer cameras for shooting images, but the Booksnap is no longer available. The Planetary or Overhead shooting tower that uses a Cell phone cam or a dedicated image sensor built-into the tower is becoming more popular, Fujitsu makes one one high quality, but it appears a bit slow and its still quite expensive.
For Step #2 you will want to break it down into Prep work before the OCR, then Post work after the OCR and finally Binding or Publishing the eBook to a format of your choice. Scan Tailor, BookDrive, and others are for Prep work before the OCR, they let you adjust contrast, tease out image artifacts or correct for under/overexposure and the "bleed through" bright lights and thin pages can bring out from the opposing side of the page that was imaged. OCR requires either the freebie copy of whatever a suite gave you (not usually a great bargain) or using a professional quality OCR like Abby Finereader, and then human proof reading the results of the OCR (if you care to.. but most people don't) then saving the images and OCR results into a single PDF file. Then you'll want to think about Binding or Publishing.. which could mean a lot of things.. to some it would mean.. using Adobe Acrobat to add accurate hyper links on Content pages and Index pages images in the PDF that immediately take you to those pages. Once all that is done.. you can simply save and use the PDF files.. or choose to reduce them to EPUB format, which is readable on most portable eBook readers and in many browsers natively.. although the Chrome Browser will read and display a PDF file just fine.