knocking while accelerating

What is your question?

ok. i have a 2007 ford fusion. an like a asshole i never did my regular oil changes. i did them about every 10000 miles. i know not good. but the oil was never low an never really dirty. anyway i resently started hearing a loud knocking while im accelerating. it is more noticable while in 1st threw third gear. i was wondering if what im hearing is a valve tap an what the possible cost of replacement would be?