Allen:  I have 4 scales, one in each apiary; AND WOULDN'T DO WITHOUT THEM!
The scales were used in hardware stores years ago to weigh feed, nails,
shingles, etc. They are referred to as PLATFORM scales, where the platform
size is perhaps 20 by 30 inches, more than enough to sit one bee colony on it
permanently and weigh it every night (all bees back home).  When it starts
gaining 2-3 pounds/day, the nectar flow is starting, and (dependant on your
location) a strong nectar flow gathered by well populated colony might
increase in weight 15-20 lbs/day.
$1500 is about right for a NEW fancy one.  Watch the newspapers for FARM SALES
and FARM AUCTIONS and you can usually get one for $50-$75.  Clean it up, PAINT
it with GOOD paint, set a colony on it permanently.  I keep my weight bars and
movable weights covered with heavy plastic waste bags from July to next March,
and then remove this cover material for weighing every day in April, May, &
June.
I have been questioned in the past about weights of 15-20 lbs per day
increase.
Remember, we are weighing thin watery NECTAR, not honey.  I have seen 30 lbs
in one day a couple of times in my life.  George Imirie in Maryland