Direct Mail
A version of this appeal was sent out by a homeless shelter (for people) during the Thanksgiving season.  There are several elements to the package and may make the mistake of appearing too costly for a needy organization.  Some printing options will keep those costs down:
Run a 2-color print.  This means simply that you’re printing on a paper of your choice in black and a shade of yellow/orange/red. 
Choose a reasonably priced paper.  The appeal looks best on a texture or heavier-weight, but will translate closely on a lighter weight and smooth texture. 
Gear all the elements down so they’ll fit comfortably into a #10 envelope.  The homeless shelter appeal used a #11 envelope, which only made me wonder where such an organization got the extra money to sink into a luxury like that. 
Do as much of the appeal as possible “in-house.”  That means the assembling and the merging of names.  It won’t lose any dignity by your taking care of everything possible on your own.  In fact, you might consider adding a note to your recipients that the organization’s volunteers did much of the appeal’s design and assembling on their own.  I don’t need to explain why that would impress a prospective donor.

Email us if you'd like a hard copy of the entire appeal, showing layout, text, etc.  This is free, and you have permission to edit the appeal to suit your needs. 
Autumn Appeal #1
Your letter/message goes on this page.  The donor's name on the reply insert below will show through the window in the envelope.
The reply insert is used by the donor to accompany his/her donation.  This insert is a duplex (2-sided) print, with a 3-up layout on standard letter-sized paper..  The mail list names would be merged onto it.
An optional "sharing" card invites the donor to share personal words of wisdom about animals.  You could post these replies on a bulletin board or use them in other campaign or appeals.