scanner for scanning seedlings
 

I am interested in using digital imagery to measure seedling growth
(the seedlings would be in petri dishes, not soil). I don't have much
cash and need to buy a scanner that can scan the petri dishes with the
lids on. So I need a scanner with a transparency adapter (a top light
source as well as the bottom light source).

I've looked around a lot but the array of products available is kind
of bewildering to me. The journal paper I am using to cite for
methodology is several years old and they used an HP Scanjet 4c/t
which I believe has a 600 dpi resolution. This machine is totally
obsolete now but I've no clue as to what would be best. I know this is
maybe a weird topic for this forum but maybe someone has experience
scanning roots/plants and would be able to recommend an inexpensive
scanner.

Thanks!