Can anyone suggest where to look for budget accommodation for 4 adults in and around Heidelberg?

We are without car and have too rely on public transport/foot..

Define your budget and how far you want to be from the Heidelberg Hauptbahnhof, else someone will suggest a €150 a night place at some random village 10km outside of town (technically near Heidelberg).

In Heidelberg will be the first choice but something in 30 mins public transport is also doable.
I am not aware what are typical costs but will prefer to keep within 100 euros.
Thanks

The NH Hotel or if you want to spluge a bit, the Bayrischer Hof.

You might take a look at HRS.com. You can sort hotels by distance from the town center or the rail station. I have found their customer "Evaluations" (often numbering in the hundreds) to be accurate and the information to be thorough. We travel by train in Germany and use HRS almost exclusively for our reservations.