For international guests, flying into Budapest (Budapest Ferenc Liszt International Airport) and either renting a car, taking a taxi/uber, or riding the train to Szentendre are your best bet. Szentendre is easy to reach via car or train from Budapest. The train (H5) comes about every 20 minutes and it takes about 40 minutes to arrive if leaving from Batthyány tér (on the Buda side, directly across the Danube from the Hungarian Parliament). We may be able to coordinate some carpools for international guests with local friends and family, so this is another option depending where you are staying.
Airbnb options are fairly limited in Szentendre, but there are a few hotels available. All accommodation options fill up quickly in the summer months due to the touristy nature of the town, so if you know you’re coming, best to book something as soon as you can. If you don't find a decent option in Szentendre, keep in mind there are many more options available in Budapest, which is only a 40 minute train ride away.