? 
Yeah 18 dollars is quite normal . Quite a few Nepalese(few thousand) work as a office cleaner and get average of 30$/Hour .These days thousands of Nepalese work as a aged care worker and average is about 25/hour. MacDonald and KFC pay about 17-18 /Hour . Average suburban cafe pays no less 15-16 dollars.
//Do I have to get new financial documents or can I still use the previous ones.//
Yes you have to make new one. Only SBI bank and NABIL are approved for Australia VISA .
//It is much better and safer to apply from here
rather than going to nepal and doing the same. But where will I need to
go for that?. US embassay/ Aus embassay or any consultancy or contact
the Aus college straightly.//
95% Students ( AUS has 500,000 Internation students compared to about 550,000 in US ) apply thru agents when applying for Australia Visa.But you can contact UNIVERSITIES directly first for offer letter and contact high commission or AUS embassy in DC for visa processing .Please note its quite tricky to apply AUS visa.
Its better to apply in US cause there are overzealous visa officer in New Delhi and they will reject your visa for no reason.