Best cheap large format negative scanner

[Nokorola]

Hello everyone, I'm new to this forum, but I hope to stick around for many years.

I am looking for a cheap way to scan hundreds of 5x7 and 8x10 negatives as an act of goodwill for my local library. These negatives are a range of ages, but mostly from the late 20s until the late 50s. I have been putting this project off for about two years, and now that I've started I've come to realize just how difficult a process it is. I have an Epson Perfection 2400 Photo scanner that I was given, and while it works, as several of you may know, it is made to scan slides and 35mm. I have tackled this issue as much as possible, even improvising a holder, but the fact that the b&w negative setting only scans an image roughly two inches wide is seemingly insurmountable. For some test scans and some particularly important negatives I've traveled down copy and paste road and pieced the negatives together from multiple scans. This gives a mostly effective negative (see attached), but is very slow, and is therefore no way to tackle the remaining several hundred negatives.

So anyway... I was curious if anyone knows of an inexpensive scanner that I could use, as the few I've researched are nice(such as the Epson Perfection V700), but bottom out at about $500, a hefty price tag for a small-town public library and/ or a college student.

Any help with my predicament would be greatly appreciated, and until then, I'll keep grinding along with what I have.

Thank you sincerely for any help,
-Phillip

ps.
I was toying with the idea of taking an older/free scanner and cutting/disconnecting the portion of the cable that illuminates the scanner head, and then lighting the bed from above. Is this even worth attempting, or am I barking up the wrong tree?