cage for daily sunning

My bird vet suggested that I take the birds outside a few minutes daily whenever possible to get some sunshine. I am enjoying this. It gives me an excuse to sit outside in the early morning.

We brought home the cage we had at school for when we would take the little guys in for a visit. It is about 18" square, slightly smaller in one direction. I only stay out between 30 and 60 minutes daily. Daisy, the maximillian, and the three little birds all get along well together in there for that amount of time. It has a food cup and a water cup, two perches and a boing, none of which are really the right size for Daisy, so I might put a fatter perch in there. (In typing this I remembered I already have one in the drawer, anyway. :doh There are probably not many 200 gram birds that could be trusted with three 40 gram birds, but, if anything, they bully her, although for that period of time I'm not worried about it.

Then there is Roni, the senegal, who must be by herself. So far I am taking her in the travel cage, but it is very small. I'm estimating something akin to 12" X 6" x 6". I have a little crock I can put in there for water, and I can give her some veggies. My question is whether or not this is too small? I do use it for her for trips in the car, and they are that long, but not done on a daily basis.

The cage I put everyone else in is unhandy to move in and out and store, so I wouldn't want to go any larger than that, and even smaller would be better, but is the travel cage too small. Additionally, I don't want to spend much money on this if possible.