I'm assuming since you are doing full boil batches that you also have a wort chiller?
You literally only need a mash tun; that's all that standing between you can All-grain. Since it sounds like you don't have a ton of time to build a full-on temerpature controlled recirculating mash, I would recommend building a mash tun out of a cooler.
Get a 10gallon (round) water cooler, or a 48QT or larger rectangular cooler. Follow this guide:
Converting a cooler to a mash tun - Home Brewing Wiki
Shouldn't take more than 1 hour of your time, and cost less than $60. I had a rectangular one, and made a manifold our of CPVC rather than copper. I ran over 40-50 batches through it, and it still had tons of life left before I upgraded.
It sounds like you have the money for something nicer, but until you have the time to DIY a recirculating system, I'd use a cooler because it's insulated, and they work great.
Now assuming you don't mind using your boil kettle to heat your strike water, and picking it up and dumping it into the mash tun, that's all you need. If you don't want to pick up and dump, you need a March or Chugger pump ($100-140), or a stand that will allow you to gravity feed the water. You might also look into another vessel to hold hot water, and possibly another burner under the Hot Liquor vessel. But you can see how the price shoots up quick