Unfortunately there is no way to 'cheaply' get an Amiga to do modern stuff like run in 1024x768 hi/true-colour, play videos and MP3's. It will cost several hundreds of dollars, or even 4 figures if you go for PPC and graphics card, and even then it will be orders of magnitude slower than a Pegasos or AmigaOne.
And you will be frustrated as you realise you have spent so much money on a system which still can't even do today's basic tasks. Classic Amigas are great machines, but just accept that they are 20-year-old technology.
