You'd have to do the math and some serious trip planning if you want to take it far from home, but either a CNG conversion on your Kia or a CNG suburban (or similar 7 passenger stock CNG vehicle like an econoline van or a tahoe) plus a home CNG compressor that fills your car from the natural gas that goes to your house. US average price for NG is easily 1/3rd of the gasoline so (from a $$$ perspective) its like getting triple the mileage.
You'll have to do your own math with regard to local gas prices, but there are tax rebates for CNG conversions, CNG cars and CNG home compressors so factor those into your equations.
For my money though, if seating for 7 was a priority, I'd find a vista cruiser or similar 7-seater classic station wagon, particularly one with a six cylinder engine. You can probably squeeze 15 mpg out it and (at least in my experience) classic cars don't depreciate fast, if at all.
Better yet, combine the two ideas, convert a classic wagon to CNG and reap the benefits of both zero depreciation and cheap fuel.