Wait. Tomorrow is the iPad3 announcement, and it will likely be sold at the current iPad2 price right now, with the iPad2 being cut down in price. That’s how Apple usually does things.
While it’s not technically required to have Wifi to use an iPad, you will be severely crippled without access to one, or have a data connection plan. Wifi is available in a lot of places, so depending on where you work/live, you may get easy access to that for free, otherwise you will need to have a wireless router hooked up to your home internet connection.
If you want one that uses 3G (maybe 4G?) data on a wireless network then you will have to buy the iPad from that carrier, and it will be a new plan. The iPad can’t share your smartphone’s data connection unless you have a wireless hotspot device.
As for it being an oversized iPhone, it is and it isn’t. They both run iOS so they operate nearly identically, but the iPad3 will have significant more screen space and power to run more robust applications, for example Microsoft is doing a port of MS Office to the iPad, and Adobe recently released an iPad version of Photoshop.