I'm nearing the end of an NA build with mine and its all been done to a budget (mostly).
Blox inlet manifold (these are close enough to being the same as the Skunk2 inlets for a fraction of the price, I got mine second hand for £150)
DC2 integra cams and valve springs, it might take a bit of digging but you can get a set of cams for £200 and I think the springs were an extra 50.
On top of this I got an engine rebuild kit which came with YCP B16B pistons. the kit was approximatly £500 but I had to pay a fair chunk in import tax and shipping as it came from the states. it also included a full set of king bearings and seals for the whole engine.
An ebay special 4-2-1 stainless manifold with a 2.5 inch collector to go with my exisitng 2.5 inch mongoose exhaust. the manifold was about £160, The exhaust was on the car when I got it.
The car is going on the dyno in the next week or two when I get everything buttoned up finally and honestly none of us have any clue what kind of power its going to make. all we know is the compression ratio is higher than any of the factory engines, with VERY approximate napkin maths it should be nearly 13:1.
you can pick and choose how far you want to go with yours but obviously some of the mods require some of the others to work, and once you get past a certain point you really do need to Map it otherwise it will never be right.
Also bear in mind that if you do the inlet manifold it means deleting the IAB's which caused me some headaches in the beginning.
I'll be doing a full update in my build thread once I get time to sort through all the photographs.