I'm still lusting after a trailer myself also, but this is what I use for errands and groceries. They are made from empty kitty litter buckets. I got the basice instructions at http://www.crazyguyonabike.com/doc/Buckets . I have added an aluminum brace inside the bucket to give the material more stability with heavier items. These have lids so I've added velcro to hold the lids on/shut even if they are a bit overstuffed. I painted them black with Krylon fusion spraypaint that is made for use on plastic, I mainly painted them since I had litter buckets with writing on them. I bought multiple large reflectors and placed them on the back, front and outer side edges. The hooks are rope cleats purchased at a hardware store. The panniers themselves are hooked to the top of the rack and then bungees hold them into place at the bottom of the rack bracket.
The materials total cost to me (not including the buckets) was somewhere around $25 or so. I take these on the bus with me when I use public transport for my bike. Another nice thing about these is that with the lids and the fact that the buckets are level with my rack, it basically can extend the top surface. I haven't tried it yet, but I intended to see if I can tie items to the top of the rack with strapping or rope if necessary.

I can't get the slide show to post, but here is the link and some photos
http://s15.photobucket.com/albums/a3...t=3e0c0ec1.pbw