"The television is very expensive."
Translation:Cái tivi rất đắt.
There is no difference , but it is seemed as nonstandard and imformal, and mostly just occurs in spoken Vietnamese.
Yes, "rất" means very, so in English. Example: very hot, so cold - rất nóng, rất lạnh. "Quá" means too in English. "Rất đắt" (very expensive) it is expensive but I may buy it. "Quá đắt" (too expensive) it is expensive so I cannot buy it.
Yes, but you have a typo. It's "mắc tiền", and I use it just as often as "đắt". I'm not sure if it's a South Vietnamese thing or just the people around me.