Blower OD is not a magical power adder. It can help if the inlet is opened up enough to accommodate it, or it can be used to shift the power to a lower rpm, but without opening up the inlet, more than 10% OD will not yield any more power, and may actually result in less power due to the increased heat and increased parasitic loss from turning the blower faster. If an MPX isn’t in the budget right now, here is my recommendation for a good budget setup:
Buy a Magnum Powers inlet
Buy a 75mm TB
Buy or build a front mount intercooler, or at the very least a double intercooler
Spend some time porting the blower inlet
Run 15% OD with that combo and a good tune
That obviously will not match the power level of a MPX, but that combo will make for a very fun car to drive on the street, and the intercooler will be needed anyway for any future blower upgrades.
If you want to go one step further, also get an 85mm TB, 4” inlet and a slot MAF or 90mm Lightning MAF. All of those upgrades will be needed down the road for the MPX anyway, and will also benefit you with an MP inlet and ported blower. You also might need larger injectors with that combo, so plan for that.
After doing all that, when the time comes for the MPX, simply swap blower and inlet for the MPX pieces, and maybe bump the OD up to 20%, and resell your ported blower and MP inlet to offset the cost of the MPX.