Beetlejuice sandworm. There's an amusing behind-the-scenes photo of the set construction for the sandworm scene, which has a model sandworm next to a model door, the door they step out of when they try to leave the house. The sandworm's visible body is perhaps 2x the height of the door, and most of it is underground. Figuring a 2m door height, we can estimate this guy is about 20m long. Not something you want to meet in the dark, but only about 4-8 rhinos big.
Sarlacc. A real big boy, about 100m in length, unknown average diameter but the artists' depictions I've seen make it look like roughly 30-50m in circumference, or about 12-16m in diameter. Probably 400 rhinos big.
Shai Hulud. One of these things eats an entire spice harvester in one bite. Basically doesn't even belong on this chart unless this is a log scale, these guys are 15-25 metersin diameter, big enough to eat the flatbed truck and the graboid without even noticing it swallowed them. Probably a mile or more in length. Given the current state of the rhino population, a Shai Hulud almost certainly outweighs all rhinos put together.
It should be noted that while the sarlacc's diameter seems to put it in punching range of the shai hulud, two things really set the Dune sandworms apart:
Basic biology math. The mass of the creature increases with the cube of the diameter, so a ~2x increase in diameter for the shai hulud translates into a mass ratio of 8x.
Length. Shai Hulud are much more wormlike than Sarlaccs. That means they're far, far longer relative to their diameter.
Put these together and you can be pretty sure that a sarlacc to a dune sandworm is like a puppy.
EDIT 2:
I am pleasantly surprised to learn that some species of rhino have many thousands of individuals. I believe they would, in fact, outweigh a single Shai-Hulud.
In the far future, "Our time scientists discovered debates about worm sizes. The basic unit for worm measurement was a rhino." ... "What is 'a rhino's?" ... "We are unsure still. But they didn't have many."
Considering that in a picture I found on the spongebob wiki the alaskan bull worm is five Sandys in height, and that the american red squirrel with tail is long from 25 to 35 cm according to wikipedia, with the tail almost as long as the body, I can approximate Sandy as being 15cm tall.
Therefore the alaskan bull worm is approximately 75 cm in diameter, (30 in. in stupid units) putting it first in the line as the smallest
I’d say not, because they’re apparently large enough that a Krayt dragon can fit into the cavity left behind after eating one. That thing was maybe not as long as a sandstorm, but definitely as chubby