Lambert spent £23million on new players last summer but only brought in midfielder Yacouba Sylla and winger Simon Dawkins - on loan - in January.
Supporters and some former players have questioned the outlay, even though Lambert made it clear he only had limited funds to spend.
But Lambert said: "It doesn't bother me what the ex-players think. They should know better. If they have a problem they should come and see me. But the fans have been great and I understand their frustrations.
"If you ask me if I'd like to sign a Messi or a Xavi then Jesus, yes I would have done. But you can only work with what you've got.
"We tried to do a few (deals) but the salaries, phew, they were way too high.
"We couldn't afford anyone massive. We couldn't get many loans short-term because of the salaries. Can Villa not compete with the Stoke's and Newcastle's? Yeah, that's too high for us.
"But I'll say again that Randy Lerner (club owner) has been great and I knew the remit."
Lambert insists he is unconcerned about the level of spending being carried out at some of Villa's relegation rivals, most notably QPR.
He said: "I never bother. I don't get over embroiled in something someone else can do. If Harry (Redknapp) wants to do that and thinks it's right for QPR, he's got to do what he thinks is right.
"I can only affect what I can do here. I don't think 'He's brought in somebody and he's brought in somebody.'
"You can only go with what you've got and I don't have any qualms about what other people are doing, none whatsoever.
"I think there's got to be a realism at the minute. I think that's why the fans are with us, because they can see what's going on."
Lambert hopes Sylla, signed from French club Clermont Foot, and Dawkins, who is on loan from Tottenham, are given the chance to settle and both have been added to the squad for the Premier League encounter at Everton.
Lambert, whose side have gone seven league games without a win, said: "We've got to give the new lads a chance.
"It's not like they're household names coming in and everyone knows them because they've seen them play 20 times or 30 times and they know what they'll get.
"That all comes down to it being a financial thing as well so we've got to go with what we've got and give the the lads an opportunity to get going.
"The one thing they'll do for this club is give it all they've got. That's what you expect of people.
"I've seen them both play so we know exactly what we're getting. They're young players but they'll give it everything they've got for this club and that's what you need."