Arco is absolutely brilliant. I've been there many times with my wife and we do a mix of via ferrata, biking and sport climbing. Via ferrata is pretty simple really and still really enjoyable as a form of "light adventure" - have a look for the trento area guidebook on the net and you'll be sorted. Our favourite place to stay is http://www.masolizzone.com/eng/default.htmNot a budget option, but very relaxing and the standards are really high.
Rio Sallagoni is a short but spectacular one through a nice little gorge below the Castello di Drena.
where best to stay on lake garda?