Using Context free language to simulate regular expression in finite automata
No such non-trivial bound can be obtained. Consider the language $L_n = \{ 0^{kn} : k \in \mathbb{N}\}$. Any NFA for $L_n$ needs at least $n$ states, but it can be generated by a context-free grammar with only one non-terminal: $S\to 0^nS|\epsilon$.