I just changed my oil, filter, and fuel filter.
Changing oil on a Prism is absolutely a piece of cake. I bought a 16gal drain pan/tank at Walmart, Rotella oil and filter at AutoZone. All for about $70.
The fuel filter is more of a challenge. I ordered a Mann fuel filter online for $89. Mann is same as OEM filter, made in same Czech plant, just branded Mann instead of Mercedes. Don't buy a generic!
Oh, I was quoted $600 to change all of the above, and of course they wanted to keep my RV for 2wks!!! I did it all in 3hrs. 3hrs only because it's the first time I've ever done it. Probably 2hrs next time. If you've never worked under the hood, you might need help with this one. I took pictures, need to make a how to or something if no one else has. Just take your time, and most importantly remember how you took everything apart!!..so you get everything back together correctly!
(warning: there's a fragile plastic hose clip on the fuel input hose! Get that one back on right or you'll have fuel all over! Before you put the air filter back on, turn the key to the right to get the fuel pump going. If you didn't get that input hose back on right, you'll know pretty quick..., fuel squirting out all over.)
When you finish your repairs, it'd be a good idea to drive your RV around a bit. Take it to the grocery store a couple of times. Or better yet, to Cabelas, The Bass Pro Shop, Home Depot or Lowes. You sure don't want to have a problem on the day your heading out on a Trip.