I'm with Bob and pfigen as it is a false savings to not save the 16bit file. Who cares what "most pros are happy with" - you could also argue most pros have professional capture within the limits of their output medium so they don't have to worry about dropping to 8-bit. 16-bit files gives you the headroom to do what you want with the files--are all of your exposures professional captures? Mine aren't and I enjoy the 16-bit safety net for those great shots that need a little more help.
Based off of 300 rolls of 36 exposure film and based off your info that "the highest tiff file yeilds a 40-50mb file" we're looking at:
300roll x 36 exposures = 10,800 individual frames
To make sure we're not undercutting, let's go 350 rolls.
350 rolls x 36 exposures = 12,600 frames
12,600 frames x 50mB/frame = 630,000mB
It seems like a lot, but:
16bit: 630,000mB * (1gB/1024mB) = ~615gB
3x 750gB Western Digital Green hard drives at Newegg.com are $65 each today, or $195. (one at the house, someone else's house, safety deposit box like Bob suggested)
If the price difference is 40% we're talking about a saving of less than $100 and that's if you bought all 3 hard drives today--storage will only get cheaper! I don't know anything about you or your photography, Angelo, but I am going to say your photography and piece of mind is worth that ~$100 if you're going to take the time to do the scans in the first place.
That's my recommendation based on wanting "to store your images right and only once".