...Your MRC Prodidgy Express is rated at 1.6 amps so it should handle two engines easily and probably three. If you need more power, you can upgrade the power supply to 6 amps with the Magna Force MF615 for less than $40.
Adding a more powerful power supply will not increase the amperage rating of the Prodigy Express. The command station itself is rated at 1.6 amps and will shutdown if you try to draw more than 1.6 amps through it. If you need more power, you have to add a booster.
... I dont have a huge budget and would like to keep it around 250. I like the Digitrax (what everyone round here uses) but I need walk around and Digi is out of price range above zephyr...
You can get a Zephyr and a UT4 throttle for around $225.
One thing to consider with MRC, if you ever want to hook it up to a computer(for easier programming of decoders, dispatching, signal logic...) the announced interface(it's not available yet) for MRC is expensive and will only work with MRC's software(unless they have a change of heart). That being said, I do think the MRC systems are good systems and if you don't care about the computer interface situation then you would probably be happy with one.
It's hard to say if the 1.6 amps of the Express will be enough for you. Locomotives vary greatly in the amount of current they draw, so 1.6 amps could be enough for as few as 2 or as many as 10 or more (some examples: according to Model Railroader, an Athearn Ready-to-Roll GP60M reviewed in 2004 drew .7 amps when slipping, but a Ready-to-Roll GP40X from 2007 only drew .15 amps when slippping).
Personnally, I would skip the Express and reconsider the Zephyr or the Prodigy Advanced 2. Either one would be more money up front, but if you end up having to get a booster, you'll probably save money in the long run. Also, even if 1.6 amps is enough power, you would probably be close to the limit, and I don't like running electronics close to their power limit for extended periods because they tend to run hotter and are more likely to fail. Something to note - your Command 2000 is rated at 2.5 amps, so if you replace it with a Prodigy Express, you might be able to run fewer locos than you can right now.
Another option you may want to look at is a Lenz Set-90. These are 5 amp systems that run right around $250(not including the power supply, but you could use your MF615).