Arrival by plane
If you arrive to Budapest by plane, the easiest way to reach your hotel is by the airport minibus. This offers a reliable door-to-door service for a moderate price (1200 HUF = approx. 5 US$ / person). A discount is offered to those who buy a return ticket (with a precise return time fixed later).
For more people travelling together a taxi could be more economical, however the price will depend on the company (and sometimes on the driver!). The prices to downtown would be usually in the range of 3500-5000 HUF.
There is also a city bus No. 93 taking you to the end station of metro line No. 3. From there take the metro to Ferenciek tere. If you stay in Hotel Peregrinus, a short walk would take you to your hotel (at the crossing of Szerb utca and Váci utca). For those staying in the Guest House of the Ministry of Education, bus No. 7 is recommended (eastwards, in the direction of Bosnyák tér). The Guest House is at the corner with Stefánia út. (Warning: there is also an express bus No. 7 which does not stop in front of the Guest House, only some two hundred meters further. The number 7 on it is red; and there is a big 7-173 sign on the side of the bus; this distinguishes it from the regular line.) Both for the buses and for the metro one has to use prepaid tickets (90 HUF/ticket); you have to validate a new ticket each time you change to another bus or metro (i.e. these are not transfer tickets). Tickets can be purchased at the airport or at metro stations.
Arrival by train
If you arrive to Keleti pu., then bus No. 7 will take you to Ferenciek tere (westwards, in the direction of Bornemissza tér) and then walk to Hotel Peregrinus, or to the Guest House of the Ministry (eastwards, in the direction of Bosnyák tér). (The two hotels are in opposite directions.) A taxi ride could cost about 500-600 HUF (to the GHME) or 800-1000 HUF (to HP).
If you arrive to Nyugati pu., then metro line 3 will take you to Ferenciek tere. Then proceed as above. A taxi could cost slightly above 1000 HUF.
Arrival by car
To Hotel Peregrinus the best way is to go from Hotel Astoria (crossing of Kossuth Lajos utca, Rákóczi út, Károly körút and Múzeum körút, close to Erzsébet bridge) on Múzeum körút and Vámház körút; then turn right at Veres Pálné utca to the right; you can get to Hotel Peregrinus by turning left on Szerb utca. Those staying in the hotel will get free parking permit on campus of the university (some five minutes walking from the hotel, on Múzeum körút). To the Guest House of the Ministry of Education, from Hotel Astoria go eastwards on Rákóczi út, then continue on Thököly út (Keleti pu. should be to your right), in the direction of Miskolc (M3). Cars can be parked at the yard of the guest house.
The Mathematical Institute is within 5 minutes walking from Hotel Peregrinus. From the Guest House of the Ministry of Education you can take bus number 7 (westwards) to the stop Astoria or Ferenciek tere.
At present the middle exchange rate is approx. 1 US $ = 240 HUF. Foreign money can be freely converted to HUF, but keep the receipts in order to be able to convert back without difficulties. Most banks and exchange offices offer similar exchange rates with no comission charged for the exchange. A few offices have good rates only for large sums; please, check the gap between buying and selling rates (it should not be more than 5-6%).
Citizens of most European countries, Canada and the United States don't need a visa when coming to Hungary. To be on the safe side, please, consult your travel agent or the closest Hungarian Embassy.
Here are the relevant parts of the map of Budapest: