Random pick:

1) cheap - barato (!) (Same as native language's)
2) expensive - caro, costoso (Costoso)
3) frugal - frugal (!) (cognate)
4) add - agregar (makes sense)
5) take away - llevar (!) (I've been using this all along as a translation for "to go"
6) replace - sustituir, reemplazar

(!) - means I'm surprised