This is What I ended up with.
Step 1: Overview
You can see the basic idea; build two halves that are 31" x 85", the extra three inches are to make room for the braces at the head and foot to reduce sag after the two halves are bolted together. The slats sit loose on the frame, and are connected to each other with a nylon strap stapled to the bottom so they can be rolled up and moved as one.
Fully dismantled there are five components, but I haven't decided on a headboard yet, so that may be added later.
The frame is all pine to reduce cost because you don't see much of it anyway, and facade is oak.
Step 2: Materials and supplies
2x) 8' appearance grade 2'x2'
6x) 8' 2" x 3"
10x) 8' 1"x4" *
* I was looking for the cheapest material for the slats and furring strips are cheap, but no good for building since they had no smooth sides, but the appearance grade 1"x was all $6+, then I found these 1" x 4"s that were called heave, or hearty, or something like that, and were finished on 3 sides, actually 1" thick, and only $3.68
Total was about $50
Oak: 3x) 1"x8"x8'
Came to $65 from the local lumber yard.
A couple lengths of 1/4" bolts with washers and these furniture nuts that sit flush on the wood with the thread inside the hole.
A couple boxes of screws, 2.5" and 1.5"
A couple nylon straps and hooks for them
I didn't want to use any kind of metal brackets because the local Ace is way overpriced, so I did everything with wood and screws.
The total for the hardware was about $25-$30
1 Quart satin polyurethane
1 Quart "classic black" stain
1 Quart "red oak" stain
some 220 sandpaper
a couple foam brushes and a bag-o-rags
totaling about $35
All together I spent around $180
Step 3: Putting it together
The outside 2"x3" has a notch routed out along it's length for the slats to rest on, so they are aligned with the bottom of the 2"x2", but the slats rest on top of the inside 2"x3"s , so they are aligned with the top of the 2"x2"s.
The two halves are bolted together, and then there are pieces of 2"x3" at each end bolted on to support the center and spread the weight out to the corners of the bed when it's all put together.
The feet are made out of the leftover bits of wood and I cut them at an angle to give it a more slim look, rather than looking like a gigantic block.
Step 4: Making it nice
Since the oak at the foot couldn't be attached to the oak on the sides, I had to come up with a way to obscure the corners, and you can see what I came up with.
Those accent pieces are screwed onto the side pieces and just sit flush against the front piece.
After working out all the technical details, all that was left was to take it back apart to finish with stain and polyurethane. The black stain actually looks pretty good on the pine IMHO, but I put it on a bit thick in some parts.
I didn't want to put any finish on the slats incase it would bleed into the mattress, and it had already been delivered by then, so I was anxious to finish; so I just softened all the edges with an orbital sander, and then sanded them to a nice smooth surface.
Last thing I did before taking it apart again to bring it in was to lay out the slats so I could staple them to the nylon straps.
Step 5: More pics and final thoughts.
Some other ideas I was toying with were some built-in storage for extra bedding, and casters that tuck out of the way so it's easier to move for cleaning and changing the sheets, but for now I just glued those plastic things on the bottom of the feet, and the mattress it so light that the whole thing is actually pretty easy to move as is. The only other thing is I will probably need to add a center support fairly soon, I was just too anxious to sleep on my new bed to bother at the time.