There is an old but excellent scanner that can easily be found on eBay for under €100. It is the Agfa Arcus 1200. This scanner is notable for its large transparency unit, which can even handle 4x5 negatives, and the fact that it scans film/negatives
without a glass platen
.
Here is a fairly detailed description
:
http://www.photoinfos.com/Scanner/agfaarcus1200.htm
Hamrick Vuescan is a decent, up-to-date scanning software for this device, available for both macOS X and Windows.
The only drawback: the required SCSI connection.
Retrofitting this in desktop PCs is no problem, but with laptops you must use either a USB-SCSI adapter (not without its issues!) or a CardBus-SCSI adapter. For Macs, a FireWire-SCSI adapter would also be an option.