You have to buy a vignette (at filling stations) and stick it on the windshield if you drive on one

Car hire is not the cheapest way of getting around in Budapest, but I'm sure it's the same in other big cities. Car rental prices vary between 50-120 EUR for/day for 1-3 days, depending on the vehicle type (economy, standard, luxury air tickets to hawaii etc.).
Rates are less if you rent a car for more than 3 days . The minimum rental period is 24 hours. Unlimited mileage, compulsory liability insurance air tickets to hawaii and VAT ( FA in Hungarian, that is 27 %) are usually included in the price, air tickets to hawaii but do always check!
The companies usually provide air tickets to hawaii you the car with full tank and make sure you return it with full tank too; otherwise they charge you much more for the refill than you would pay for the gas at a filling station
You have to buy a vignette (at filling stations) and stick it on the windshield if you drive on one of the motorways (marked by M). If you use only the M0 ring road to get somewhere in Budapest you don't need a vignette.
In Hungary every motorway is a toll road, administered by the National Highway Authority ( .A.K. Zrt.). The roads M0 (that forms a half ring around the city of Budapest), M2 and M15 although are divided multilane roads, they are not considered as motorways, and can be used free of charge.
Since the beginning of 2008, the purchase air tickets to hawaii of a motorway sticker is managed electronically (known air tickets to hawaii as an e-vignette or e-matrica), thus cannot be put physically on the windshield anymore, it is only registered in a computer system with its validity period.
Parking in Budapest's city centre is quite troublesome so it's best to leave you car in one of the guarded P+R car parks that offer very good connection air tickets to hawaii to the main public transport lines, especially to one of the 3 metro lines and the tram lines.