It depends how much GP you have as well. To reach 450, it's a must to use Discerning Eye with the Appraisal which costs 200gp. With 400 GP you get already two Discerning Eyes with Methodical Appraisal. I don't know the numbers that are required with Perception, but it has a cap. But if you can't reach 450 collectability with your current gear even with DE boost, you just have to make gil to better your gear. ^^;