IOS – Do we have to submit a Paid Application Agreement if I intend to fix a price for the app @ 0.99$

The App Store doesn't offer that functionality by default, and you can't configure or script it to check for updates. So...

The closest you're going to get is automatically opening the App Store so you can look at the icon to check for updates. Here's how to make the App Store open automatically at an interval:

Open iCal and add a new event. Call it something like Check App Store for Updates. Double-click it on the calendar and click the Edit button. Set the repeat menu to Every day or Every week.
You can get it to check at some interval in between (say, every 3 days), by using the Custom... option.

Set the alarm menu to Open File. In the newly-showing second menu under alarm, choose Other... and select the App Store in your Applications folder. Set the last menu under alarm to on date.

This way, iCal will automatically open the App Store at the interval you specified under the repeat menu. Its window will pop up to remind you to look at its icon. When you do, you'll see the number of available updates.

Run on PhoneGap on a PC until you hit a roadblock.

You can always post here on whatever specific roadblock you hit, but as the iOS toolchain has matured, you don't necessarily need Xcode to make an app anymore.

• RubyMotion (non Xcode solution, but still requires a Mac OS)
• WebApp frameworks
• PhoneGap and other frameworks

So, you have dozens of tools to start and once your delay to development costs you more than the $250 it might cost to pick up a used Mac - you can decide to buy tools that make your development move faster or cost less due to quality or other costs to development that better tools will reduce for you over time.