According to Aguirre, Espanyol are in the bottom three in the Primera Division in terms of outlay during pre-season, having only brought in a handful of new faces so far while welcoming a number of other players back from loan spells.
However, the former Mexico coach does not believe that will equate to the team struggling on the pitch this season.
Speaking ahead of Monday's season opener at Celta Vigo, he said in Marca: "I'm very happy with the dressing room that we have, even though we are among those who have spent the least. We are in 17th or 18th place in terms of signings.
"We've only spent 250,000 euros on reinforcements, but we will compete, and well, against everyone, against Sevilla, Valencia, Real Madrid, Celta...Let there be no doubt about that."
Regarding Celta and their new coach Luis Enrique, Aguirre said: "I've never spoken with him (Luis Enrique) but I know his career well as a player and a coach. I know he's a brave guy and a winner, so Celta will be brave and give it everything.
"It will be a difficult game, we haven't forgotten the match we lost last season."
On that occasion Celta beat Espanyol 1-0 on the final day of the campaign to dramatically avoid the drop - they finished a point above relegated Real Mallorca - but it was not enough to save coach Abel Resino, who left the club by mutual consent in the summer before being replaced by Luis Enrique.
The former Roma and Barcelona B coach will take charge of his first La Liga match on Monday and he is in high spirits.
"The team have arrived in good condition. I'm happy with the attitude of my players. Tomorrow is the day. I'm optimistic because I think my team has improved," he said.