Hi,
I live in Hungary and I think I know the market. It would be a long story for one single post, and also, offers change every other day
All I can promise right now is that if you tell me what you want the best option for, I'll try to give you hints.
Mobile internet is not cheap, but a lot depends on how much traffic you want to generate. You can get dedicated data SIMs, or you can get mobile data bolt-ons with a certain amount of traffic.
As for dedicated prepaid data SIMs, all three providers have offers, Telenor has hidden their offer, it is worth taking a peek at 'Djuice Reload Net', which is an alternative to Telenor's own, minute-based offer. Unfortunately I cannot find a link in English, perhaps because their target audience is local youth
T-Mobile and Vodafone both have their flexible prepaids, where you pay for the amount of data you use and not a fixed monthly fee, but these offers are meant for people who only use the card occassionally and do not generate a lot of traffic. Like me. If you know for sure that your traffic will exceed a certain limit a give month, you might be better off with a normal voice SIM with a certain amunt of prepaid gigabytes.
People are different, and the choices are abundant