Few quick things

well if its basically stock car.. and you only have 400 to spend... I would shop around for a stock radiator. Considering a new aftermarket radiator is going to cost you alteast 200 plus... as for the cold air intake... http://www.jegs.com/webapp/wcs/stores/servlet/product_10001_10002_744980_-1_10435 here is what the cold air intakes are... its basically just the air inlet to the intake... few extra hp and looks alot nicer then the stock air intake... as for an intake.. few intakes u could go... trick flow makes a few... edelbrock.. bbk.. and the cobra intake... all pretty good intakes.. but seeing as your money is limited.. you could go with a TYPHOON intake.. basically its the edlebrock intake... but its made overseas.. and not as good as quality... but better then ur stock..
my best advise.. look in the parts section... you can find some quality parts for half the price of the new stuff... good luck with your car.. have fun and stay out of trouble.. or that 400 will go rather quick..

I would suggest getting away from the stock radiator. It will be fine for a stock motor but if you do have plans for upgrades in the future, which it appears, it leaves little room. I suggest a griffin generic 31x19. Northern/Summit racing also seems to be a popular choice with great feedback. The Autozone 3 core brass/copper radiator seems to have served people well too. Both are about 200 bucks from summit. Cold air intake for our cars unfortunately doesn't do much other than clean up the engine bay. The stock air box is essencially a cold air intake since it draws air from the fender. Untill you get into some serious mods or like the look, the best option is to get a K&N panel filter and call it a day. Some people run into issues with cold air intakes due to how the MAF samples the air going through the 90 degree bend to the fender. Just a thought. As for intakes on a budget, I suggest getting an intake from a 5.0 explorer. These are extremely similar to the cobra/gt40 intake which when the time comes, can be ported for more power. Another thing to watch out for is though an intake like the TFS and Holley boast some good numbers, down low they are pretty lacking without some heads and cam to compliment them. For a stock motor with stock heads, stick with the explorer/gt40/cobra intake or the edelbrock/typhoon. The typhoon casting is a bit rough so you may want to clean it up a tad before installing it.
Kevin

If you plan on future mods for power than I would get a aftermarket rad. I bought a 3 core Milodon for about $225. I am happy as I know my car will never see more than 300 hp at the wheels. With what is left you need to decide what is more important at this time of year. A/C or intake. I don't know of an intake worthwhile that is less than $380 anyway. Maybe some subframes or other supporting mods with the leftover.

400 dollars won't go very far. I would look for a used intake or have your stock one ported by www.tmossporting.com
Kevin

I was thinking of a cold air intake myself, the only one i read on here that is maybe worth while is one that moves the filter inside the fender, read alot on here about fan wash affecting the maf readings also. most of the guys pretty much feel the stock airbox is fine for a stock/mild motor so I'm staying with it and spending money on suspension stuff. maybe a good way for you to go also.

The question you need to answer, is what is your plan for this car. If you need a radiator, you should definately get one, but the plans for the car's future will decide the radiator you should get. Its better to do it right the first time. As far as the rest of the money, an intake manifold and a cold air intake are completely different parts. Changing the intake manifold on a stock engine is not going to provide a lot of benefit unless you change the heads and the cam as well. I would wait to do those three things together. As far as the cold air intake, I would probably wait to spend the money. I agree with greensvt21, suspension upgrades would be a good choice. Everyone likes to get the engine all hopped up first, but if you don't have a good solid car/suspension it doesn't matter. If you list some more details about the car in your signature we could provide more input.

Good Luck!