Mate, i don't know what its like in your area in spain but in england there is loads of places you can pick up a complete reasonably priced bike for trials. If your in no hurry to jump into trials and would like to practice a few tricks and see how it feels get yourself a cheap 26" bike from the local newspaper, market, or a second hand bike shop... failing that ask around your friends see if they have one they don't use anymore. Once you get one (if you get one) make cheap changes like, removing/lowering the seat.... drilling the rims, changing any suspension to rigid forks and your most the way there. After that you could either upgrade that one or save for a new bike/build if your enjoying the trials scene or if not... sell it again in the newspaper/market/shop or to friends. Hope you get something sorted Keep us posted if you do i would like to see what you got! Peace