I would second the use of Unity. However, the free version does not build to mobile. You can still work on your game in the mean time, and then choose to purchase the Android/iOS build ability after you feel comfortable its a a good stage to start demoing.
The prices are
- Unity = Free,
- Android Build Addon = 400$
- iOS Build Addon = 400$
Additionally, if you want the pro route, for Pro Unity, Pro Android and Pro iOS packs, it comes to around 4500$.
Those are per person prices.
Again, I have interest in building my unity game out to tablets/phones as well, but I'm building it in the free version until its a good point to demo, and then possibly try a crowd funder to pay for the licensing.