The cheapest route like others have said is probably to buy a V6 Camry.
However since all Camry's have rev2 5sfe's with the knock sensor you can build a low boost turbo setup for pretty cheap too. Use the CT-26 turbo from an MR2 or Alltrack, 315cc injectors from a MkIII Supra, gen2 3sgte map sensor, boost controller, and all the piping, hoses and things needed to hook it up like a 3sgte. Upgrade your fuel pump and clutch too. As long as you stay below 10psi it will work and is pretty safe and it gives you 170-180whp. Go above 10psi though and you break ring lands so don't. Also if you use any other components you need bigger injectors and at least a piggyback if not full blown EMS. One last caution boosting a stock 5sfe is that you can't take it up past 17-18psi because of the ring end gap even if you have the fuel and tuning to do it.
I ran this simple setup on my stock 5sfe for 6 months before my oil pan split and leaked all the oil out. No signs of detonation when I pulled the motor apart. The biggest problem I had (other then a broken oil pan) was finding a reliable used CT-26 because most of them are just beat to death. Because of that and the fact that these setups are put together by their owners I would also not trust it as a daily driver until it had been running a while. It's always a good idea to have a second car if you mod the first one anyway.

Many people have done this setup on MR2s and Celicas and the main things that killed them were over boosting and oil leaks. If you want more info I can show you where to look or answer any specific questions you may have.
You could also build an NA 5sfe with 150-160whp but that will run you $3000+. V6 or turbo fits the Camry platform better anyway because there is more car to get moving.