It's a good idea. once you get bored, you can easily add forced induction, since the motor will be built to handle it already.
cost can range from $500 to several thousand dollars, depending on how much you do to the motor, and the hours involved in the build.
Speed is a question of money... How fast do you want to go?
Here's some ideas for you.
Cylinder deck sleeve: You need one of these, it closes up the top end of the cylinder block. it eliminates cylinder flex, and will make your motor a LOT stronger, so it can handle revs better as well as nitrous & forced induction.
new pistons (lots of companies make these): go forged pistons. you can go low compression or high compression, depending on what you want to do down the road. Don't forget the total-seal gapless piston rings! Get some new connecting rods too if you can find them. Pistons can be oversized as well for more displacement.
hardened Titanium valves: Lighter than stock, and hardened to handle the abuse of high revs. can go oversized as well, bigger valves flow more air and make more HP:
Double valve springs, titanium spring seats: lighter than stock spring seats let the motor rev up faster & with less resistance. Double valve springs will make sure those valves seal and don't wobble.
Anti-pump lifters: these hydraulic lifters will not stutter under high revs, unlike stock units.
Forged roller rocker arms: Less friction in the valetrain, usually lighter than stock. use with new cams for sure. Waiting to find these for our applications.
New cams: needs no explaination, they change timing, lift and duration of stock cams. ask the professionals to help design some to fit your needs, or go with pre-made aftermarket units.
New bearings & main caps: heavy duty forged main caps will strenghten the bottom end a lot, keep that crankshaft from floating, and handle many more Revs. the toyota bearings just suck ass for racing, get some aftermarket pieces.
Deck sleeve replacement: cylinder sleeves are not removable on the 2ZZ, they are laser imprinted on the aluminum cylinders. aftermarket kits eliminate the cylinders by machining them out of the block, making indents in the bottom of the block to accept the new steel sleeves, and a solid deck as well. way sturdy, way expensive, but easily matched for overbore pistons.
Crankshaft work: You can do a simple crank grind, where they regrind journals, balance the crank, and champher the oil holes. Or, you can go elaborate, and knife-edge the crank. this weakens the crank a little, but reduces it's weight, so the motor will rev to redline a LOT faster. I don't rccommend it, unless going to all out race the motor.
ARP fasteners: strong as hell, won't come loose, these suckers are bomb-proof!
Deck the block: shaving a little metal off the deck will bump up compression, make more HP too. Adding thicker metal head gaskets later can redice the compression if you need to. Only experienced shops should deck a block for you.
Porting/polishing the head: Regrind of the nooks and crannys of your head to flow more air, this should accompany a head build. porting is a nessecity if you are adding oversized valves.
Lastly, you will need to customize the fuel management to work with your new motor. this can include new injectors, fuel rail, a new computer w/custom programming, fuel pump, etc.
Also, look into a new oil pump, aftermarket oil pan with deep sump (try morosso) and an aftermarket water pump. if you build up a motor, the tuning will need to be changed to handle the mods and run properly.
Get pros to help you out, you'll thank yourself later. and don't forget, there are lots of books about engine building and they are well worth the read as they are very informative.