Since your goals are to save money and to only bike a short distance from "Car" to "Work", I'd say that your priorities should be (in order)
-Small. 16" wheels preferable to 20". If you're a (pardon me) short rider, you'll appreciate the smaller size. Your car will too, and you'll be less likely to have to win a semantics argument at the front door of your job ("It's not a bike, it's just bike parts, now that it's been disassembled...")
-Quality. Don't get something el-cheapo, like a no-name folder just because it has small wheels. Give preference to companies that have been around for a bit, and who have a track record for product support and customer service.
-Price. If you can get in for less money, do it. Don't ride this curve all the way to the bottom, or you'll be buying a Walmart-quality bike and it likely won't last. However, you won't be saving money if you spend $1200 on a superb folder that you only drive between the parking area and work, in order to save $??.?? per year on parking.
I'd say that the DT mini is a safe bet, followed closely by Brompton, then more distantly Stida, then Mobiky.
Don't base your opinions on the smaller-wheeled bikes on only a 1/2 hour ride around a few blocks. If you're used to riding larger-wheeled bikes, it'll take a bit of getting used to the feel of the smaller wheels. Many folks report that the smaller wheels feel "squirrely" at first, but within a short time feel "responsive" instead. If test rides are available, see if it is possible to borrow them for 20hrs... rent them if necessary. Test them out for a good long ride, test the fold, see what they feel like to load and unload from your car... wrestle them through the door of your house/apt.
Good luck with it though. Follow up with a review and your opinions of whateer you do test out or buy.