I will be going to Tokyo and the Kansai region in the first 2 weeks of April and am hoping to stay one night in Nikko to do both the temples and the National Park.

Any recommendations for ryokan in Nikko?? Budget preferably not more than 25,000 per person per night.

Also is Nikko an onsen town? If so an ryokan with onsen would be perfect.

Nikko is a classical day trip from Tokyo, so why not stay there?

Because the OP wants to visit both the national park and the temples, and you can't sensibly do both in one day? Nikko's a fair hike from Tokyo as it is, it's 4 hours on a train just to get there and back.

Nikko itself is not an onsen town, but Chuzenji about 30 minutes away is, and it's the main gateway to the national park as well. There are a bunch of other hot springs in the vicinity, just stay away from Kinugawa.

I do agree that a day trip from Tokyo to Nikko is bit difficult task, because of roads heading to Nikko and rail service it takes longer to get to Nikko from Tokyo than observing distance from a map. If you are planning to do just Toshogu temple only then I think day trip to Nikko from Tokyo is possible. However, if you plan to go up Iroha-zaka and onto Lake Chuzenji then further into Senjougawara and Yumoto area then a day trip from Tokyo become very difficult.

jpatokal is right, Nikko is not particularly known as onsen destination but there are onsen in Nikko area. One is at Lake Chuzenji (Chuzenji-ko) where you find Chuzenji-Onsen (Chuzenji Hot Spring). Going further to Yumoto area where you find Yumoto-Onsen (Yumoto Hot Spring). Looks as Yumoto area has most number of onsen ryokans in Nikko area.

Yumoto Hot Spa