The easiest way to search for fares is to use this 'trip planner': http://trips.metro.net

If you enter into the above site a starting point of 7th St/Metro Center (which is the center of downtown L.A.) and you enter an ending point of Disneyland, the result looks like this:

Starting at 7TH ST METRO CENTER

Ride METRO EXPRESS LINE 460 [DISNEYLAND] heading south

From: FLOWER ST/7TH ST SW corner Lv: 07:26PM

To: HARBOR BLVD/DISNEYLAND EAST MAIN SHUTTLE ENT NW corner Ar: 09:14PM

Pay $2.50, Monthly Pass: $122.00, EZ Pass accepted

As you can see, the fare is $2.50. That is more than the 'standard fare' which is $1.75/ride (on most metro buses and on all metro rail trains). The DAY PASS allows you to take as many trips for $1.75 as you please in one day. Since this trip is $2.50, you'll need to pay an additional 75-cents to the driver of the bus in addition to using your DAY PASS.

I would recommend that you look over the L.A. FAQs link -- the second link in the 'list of postings'. There, you'll find a topic about "Public transit" and a sub-topic of "Local Transportation". Here's a shortcut to that content:

https://www.tripadvisor.com/Travel-g32655-c171690/Los-Angeles:California:Getting.Around.html

This explains the use of the TAP (transit) card. In this content, it's recommended to use a different website to look up routes but I would recommend the one I cited above. As you'll see in the content, you can either pay the additional 75-cents in cash to the driver OR you can load onto the TAP card cash that will automatically be taken from the card whenever you travel on a route that costs more than $1.75. (BTW, it's really unlikely that you will find many of those!)

FYI, the 460 bus does stop at Disneyland and is relatively inexpensive but it takes a long time to get to Disneyland from L.A. It also passes through some 'not so nice' neighborhoods so I would not recommend riding this bus at night. Our L.A. FAQs link (cited above) has a topic about theme parks which lists many transfer options for Disneyland.