Hi from the Manager of this group. Nice to see my efforts are of some help. I find staying in Venice too expensive, much cheaper to stay on the Lido De Jessolo or even inland at Treviso or Padova where the hotels are much less expensive. Venice is easily reached by train or as we do by car. You can then also have a trip up into the mountains which are well worth it for the scenery.
It's also worth considering somewhere more South such as Rimini (much too busy and noisy for us) Riccione (campers favourite), Cattolica (a bit quieter but with an excellent beach and promenade) or Ravenna which is famous for its mosaics. The train service to Venice is excellent from all these places or a much more pleasant way is to go to Chioggia and arrive in Venice (about 20 mins) from the sea on one of the numerous ferries.
From Rimini or a nearby town you are only 30 mins by local bus from San Marino well worth a visit for the views (and the duty free prices!)
As Gillijam says May or beginning of June is probably best time to visit.
Ryannair had some 99p flights (I kid you not) to Treviso a couple of weeks ago from the UK