I thought the file sizes were rather "normal", for example, in a similar case, cabbie 2.0 for iPod video uses 23.9 KB in 10 images for the volume dB (each image 2.39 KB).
Maybe the use of "." instead of "," is causing a confusion?

Just in case, 23.9 KB = 23900 bytes
Anyway, in arboxWidgets what happens is that the original images for the volume display are in different sizes; using the common part of the image in the backdrop, makes the lower volume images smaller (18,1 KB for 12 images, individual sizes go from 354 bytes to 2.59 KB). In order to make all the images the same size for using subimages, the standard size becomes the top volume image, so the final image containing the 12 subimages is 30.5 dB.
The default theme Cabbie2 loads 82.6 KB in 33 "non backdrop" images; arboxWidgets loads 96.4 KB in 47 images, but after using subimages, it would load 103 KB in a total of 12 images. The size increase is caused by the volume images converting; it is just hard for me to tell if reducing the 12 volume images to 1 , but thus increasing the total size from 18.1 KB to 30.5 KB is a good deal. [sorry for the long reply]