Address: 1087 BUDAPEST, BAROSS TER 2 - ring 14 under the AVON sign
Go to the main exit of the Keleti Train Station, look around the square and find the building which has a huge red sign on the roof: CANON (unfortunately it is not lighted). The building is on the opposite side of the bridge (which cuts the square) than the train station. Walk to that building along the left side of the square, and look for a pink AVON sign just next to the K&H Bank. Under the AVON sign there is a keypad, you have to type 14.
This is a stop on the METRO 3 (BLUE line or M3) line. Go to the KALVIN TER metro station, switch to the METRO 4 line (M4 or GREEN line) and travel three stops to KELETI PU station, where this line terminates. Pop up from the underground. From here just follow instructions from previous point A. You will need 1 ticket/person, the price of a ticket is 350 HUF.
Take bus number 200E to Kobanya Kispest - the terminal of METRO 3 (BLUE line, also marked M3). Take this line to KALVIN TER, switch to the METRO 4 line (M4 or GREEN line) and travel three stops to KELETI PU station, where this line terminates. Pop up from the underground. From here just follow instructions from point A. You will need 2 tickets/person for this travel. One ticket costs 350 HUF (450 HUF if bought from bus driver - this case always need exact money). Keep your validated tickets for possible controls! You can also purchase travel cards (24H, 72H, 7DAY). It takes between 60-90 minutes to get to the LOCOMOTIVE HOSTEL.
You can order this service at the airport and they will bring you to the building, but you have to wait until they fill the bus with other passengers (3200 HUF/person/one way or 5500 HUF/person/return).
Has a fixed price of 22 EUR, will wait for you with a sign, Locomotive.
they have a desk in the airport, the cost is somewhere above 25 EUR, depending on the traffic jams.
Finally we have some advices for you.
Best regards from Budapest!