if you really want some help with this, we need to know:
where you live, i.e. weather conditions
what kind of driving do you do - street, some auto-x or track, handling and performance of interest to you or do you want comfort and mileage?
I went to the DiscountTireDirect website and found an $836 package for an '03 wagon - 17x7 ET48 MB Weapon wheels w/225/45x17 Falken ZX512's - is that the package you're talking about? seems like a lot for the money - but I would change the tires, see below.
MB wheels are an unknown quantity to me - I own Rotas and have nothing but good things to say about them and the company.
went to SubyDude's site - did not see a Downshift package so you must be talking about a custom package they are making for you - right?
not sure if you like the look, but SubyDude's wagon-specific package with ET53 SDR's and Falken ZR512's for $1143 is a good deal if you want an all-season tire. The 53mm offset wheel will allow you to run lowering springs on the wagon with 225/45x17 tires and not have any rubbing problems. I would personally upgrade the tires to FK451's for superb wet/great dry summer performance, or the not quite as good but longer wearing and quieter ST115's.
You could also upgrade the DiscountTireDirect package to the FK451's or ST115's and have a much better handling tire wet and dry.
The Rota wheels are wider, come in tons of color options, and if you get the ET53 SDR's you won't have rubbing problems on your wagon. Both Rota and SubyDude are known on this board for providing superb customer service. I doubt that MB has the same customer commitment as Rota, and I know from personal experience that DiscountTireDirect is not as customer oriented as SubyDude. Nice cheap place to buy tires from - but they are not a Subaru specific vendor nor very knowledgeable about our cars as a company - obviously your local Discount Tire store may be better or worse in this respect - mine is worse.
finally, you could email Luke@TireRack about a package in those price ranges. They have Kazera wheels and lots of tires to choose from that would be in the same ballpark as the two you mentioned above.
lots of options out there - you need to be more specific for us to help you further...