For the most part i use 91 in mine because its hard to find a place that sells 93 in this area...there are like 3 stations that carry it. I once was a little short on cash and tried 87 octane in it and I thought it sounded horrible. It knocked real bad, bad enough to make me never try it again.
Like others have said though, the fuel is a pretty minor concern. I have a 93 that i bought in 2000 for $12K that was in absolute fantastic condition with 110K miles on it. It now has 200K miles and over the last 4 years I have had to put something like$2-3K into it in parts alone. I had to replace half shafts, timing belt, exhaust repairs, etc. Mosts of the work I did myself....well with the assistance of Eddycat and good ole Dr. Kuo (another SVXer here in KC) but it is still pretty expensive. Then of course you have the regular maintenance like getting all new tires at the same time (since its all wheel drive), oil changes and the like which i didn't include in the $2-3K that i said i have spent. Its up to you.
If you get this car, expect to pay through the nose for it. They are a blast to own and I love the attention that my baby gets but she costs me more than any girlfriend i have ever had...except Marisa
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~Ray