The EVE API definitely has the data but I’m not sure where is best to see it presented but I’m sure this site will be able to provide it in one form or another. Taking the total transaction volume and comparing it to the in-game market history tab and the orders/donchian channel dots would give you a rough estimate.
Here you can see the depth of buy/sell orders that are currently up in a station/region:
https://www.adam4eve.eu/market_orders.php
This is the sum of the total transactions of each item but I’m not sure whether you can split it up into buys/sells:
https://www.adam4eve.eu/tradeVol_type.php
Or the data for the hubs themselves:
https://www.adam4eve.eu/market_hubs.php
EDIT: Ah, what you’re looking for can be found on the commodity page for each individual item. The “order item quantity” graph. Obviously you would have to divide the number of transactions by the buy/sell price to get the figure you’re looking for and, again, you can change the range you’re looking at in the top right corner. There are little checkboxes beneath the chart to select buys-to-sells, sells-to-buys or total combined buys/sell:
https://www.adam4eve.eu/commodity.php?typeID=34
This site is fantastic although a little overwhelming at first. You can click on the little “HELP” images to get a description of all the different things on each page.