To clarify, using Marmalade you can develop, sign and test on the device using only a PC. To submit your app to the App Store you need a Mac because the software used to upload the final package exists only in OS X. I've developed and distributed various games using only a PC and a borrowed MAC to upload to the store.
You have a free license that puts a Marmalade splash screen and a small watermark on the screen. The full license's price is not as prohibitive as it is on Unity though, and for me it's the best option right now for those that doesn't have a lot of bucks to spend on a license. You can also use Adobe AIR, but it's slower.