wut are the cheapest things to upgread my 400 with im looking for more noticeable power

 

Change the front sprocket, smaller one tooth. For 12 bucks, theres nothing else which will change how it accelerates more than that will.
You can also pop off the air box lid (free), and get some bigger main and pilot jets, for about 2.50 each. This will open up the breathing, and itll gain some hp.
After these....pipe, cam

 

what jet sizes would you recommend if i take of the air box lid

 

Depending on your altitude, Id start with at least a #40, and maybe a #42 on the pilot, Which are plus one and plus 2.
Then go with at least a plus 2 on the main. 148 is stock, so Id skip the 150 and go to 152 and 154 and see how it runs....its posible youd need to go even bigger, but the jets are cheap enough, Jets are us, and denniskirk are two good places to buy jets from, and are fairly cheap, even with shipping, if you buy a few jets.