I read that somewhere...here maybe a while ago that said to use screening. From what I remember this person made their own gate using screen material and heavy duty velcro. They put the velcro on the wall and the screen. The screen material went across the opening and was attached to the wall with the velcro. The post said it worked really well and was cheap.
I myself have really wide openings and it would be very difficult to find gates so when I am not at home Lacey goes in her exercise pen. I can tell you that it has worked out great. The only great advice I can give you is to make sure that you get a very tall gate. These little ones are great escape artists. Sometimes when I put Lacey in it when I am at home she jumps so high that I can see that if I had gotten a shorter one she could get out. I also have her crate, bed, piddle pad, water bottle and toys in it and she seems to be very content. When I come home for lunch most times she is sound asleep in her crate and I have to wake her up.
Hope this helps.