We're drastically short of info here.
Specs are an absolute necessity
As it stands I'll assume mobo only, condition unknown and say $400 (shipping or pickup added in)
I see jacks on one so that covers mobo power supply and Case value.
If you want a more realistic price I'd need the specs, at least partially
Ram? Proc? Any drives?
If it's loaded a bit with a cd and two ram sticks I'd bump to at least 5-6 depending add the processor as high as 900 but not much more unless it has scsi or sas. (Then I'd go around 1k)
Sight unseen no specs I pay 50c to $1 for any atx or ITX computer, based on board and power, as just below break even.
If they work AND have some sort of protection system in place (ebay et al) that they will work, and have CPUs id say around $5-$10 per unit after tax and shipping giving you room to double your buy on resale.
Even if you need to buy drives and ram for them.
-- my grades are my own and do not represent an offer from boardsort, nor are they guaranteed. Please keep that in mind.