Sirmione and around beginning from Bergamo Airport
Ok Letty now I understand better. First of all I don't laugh because I experienced your same situation when I studied: I did my travels with limited budget.
Your question about hiring: for me is better because you can travel in freedom, without watching the clock and saying: "It's time to go, we have bus, we have train".
Anyway let's schedule again your possible travel!
First: take a look on this web site "http://www.ferroviedellostato.it/" because it gives you all the time tables and prices of 90% of trains in Italy. Sometimes you can also buy tickets on line (English version is available).
You have to reach Bergamo railway station from Bergamo Orio al Serio Airport: about that search "ATB" on website "http://www.sacbo.it/" (you will find a link on the left "Orioshuttle, click and bus!"). From Bergamo railway station you need to arrive in Sirmione by train (search your favourite time on http://www.ferroviedellostato.it/). Remember to obliterate your tickets to avoid nasty fines! You will arrive to Desenzano station (this is because Sirmione has not train station). Anyway don't worry about because the area is touristic so it is sufficient, arrived in Desenzano train station, to get info in a tourist point or go to lake and find boats to Sirmione (it is not difficult).
Prices: I wrote you about "il Porticciolo" restaurant in Sirmione: my sister and her boyfriend paid 42 euro for pasta, desserts, water, a quarter of wine, one bottle of water and two coffees. It's a sample about prices. Anyway, as always, avoid too touristic places and you could keep good food with a reasonable price. Usually pizza is cheaper but, I'm honest, sometimes I save some moneys going in a McDonald! Don't exclude to find in Sirmione a backer and a butcher's shop, buying there all you need to prepare your self-made sandwiches (sometimes I used also this way to save some moneys, but only for lunch!).
Now, what to visit.
One day in Sirmione but keep in mind to take Desenzano train station as base to begin your movements to visit: Verona (1 day), Soave (1 day). A tour by boat to visit Garda Lake is a must, expecially I suggest to visit Bardolino, Lazise, Torri del Benaco, Malcesine. On west side there is Limone sul Garda. Salò is important for Italian history but you could skip it.
Try to dedicate a day to visit the funny Gardaland (http://www.gardaland.it/en/home.php). Sigurtà Park (http://www.sigurta.it) is very beautiful, if possible dedicate a day. To reach it: by train from "Desenzano" to "Peschiera del Garda" and, from "Peschiera del Garda" to "Valeggio sul Mincio" using APAM bus line.
Ehm... I have reached the six days!
OK, these are my suggests.
Keep attention: no autostop in Italy, Veneto Region is not so dangerous but also not so extremly safe.
If you need more info you can contact me also by VT mail or with this one: firstname.lastname@example.org
Welcome in Italy!