Hi Inge, here is what i found for you on istria.info page.
(please, check the page if you want to see the houses in question) Oh, yes, i tried to find for the cheaper houses.
So, the first is the old manor house near the sea (only 100 meteres from it, actually), and with maintained garden. The distance from the city is 500 meters, and the house has it own private parking lot. In free time you can do boat trips, bowl, do rock climbing, play miniature golf, paraglide, cyclesail,.... All of this comes for the price of 24 EUR a day.
The other house that i found (under the name House 30333) is also only 100 meters from the beach and 500 meters from the town centre. It also has maintained garden, and an internal parking lot. In addition, this haouse allowws for pets, and the price is even lower, it starts at 21 EUR a day.
Hope i helped, at least somewhat