The most expensive things I bought today was a meat.

"meat" on its own isn't a countable noun, so you don't use "a" with it. You can use "a cut of meat" / "a portion of meat" etc. depending on what form of meat you bought.

I had richa fancy dinner with my family tonight, so I bought a lot of expensive meat a lot.

"I bought expensive meat a lot" = "I bought expensive meat many times"
"I bought a lot of expensive meat" = "I bought a large quantity of meat"

Rich for food refers to certain types of flavours, and generally is applied to specific items rather than entire meals. If you mean a costly dinner, usually people say "a fancy dinner"

It cost ￥10,000 yen.

Generally you include either the currency symbol or the currency name, not both.

The most expensive things I bought today was asome meat.

I had richa fancy dinner with my family tonight, so I bought a lot of expensive meat a lot.