130 to 135 is the horsepower ratings of the L28 in the 280ZX, as measured from the wheels, as opposed to the 170 HP measured from the flywheel of the 280Z.
As for power on the cheap, there's really not such a thing on any car. Speed costs money. However, the cost can be brought down depending on how much fabrication you're willing to do.
Before you start making any real mods however, a good investment would be a factory service manual. A haynes manual is good, but it covers a model range. You'll want one specifically for your car. They're available for download from XenonS130, but I personally find a paper manual handy since I don't have a laptop or a computer in my garage.
As already said, a job to fund the car would be preferrable. If you're not into fabbing your own stuff, which takes a lot of time and practice, go-fast mods for the S130 aren't cheap. But depending on how much interior you're willing to part with and what body style it is, you can get some very cheap go fast by removing interior parts, such as a back seat.
The last thing to remember is the S130 isn't a sports car, though Nissan says it is, and many refer to it as such. Nor is it a 'hot hatch' like a civic-SI. It's a malaise-era GT car. So it's meant to carry you long distances at speed, in relative comfort. If you're looking for a drag racer or something you can blast around in on the cheap, the S130 isn't the car for you. Certainly, the S130 can be made to perform admirably, but it isn't cheap to do so.