Mauricio Pellegrino feels Southampton failed to substantially strengthen their squad during the transfer window because they were priced out of deals.
Saints lost star defender Virgil van Dijk to Liverpool for a reported £75 million at the start of January, with £19.2m former Monaco forward Guido Carrillo the only subsequent arrival at St Mary's.
The south coast club were heavily linked with a deadline-day move for Spartak Moscow's Dutch winger Quincy Promes but the transfer was not completed, reportedly due to the Russian club's lack of time to find a replacement.
Manager Pellegrino believes it is difficult to get value for money in the transfer market in the wake of recent deals, including Paul Pogba's £89m switch from Juventus to Manchester United in 2016 and Neymar's world record £198m move from Barcelona to Paris St Germain last summer.
"I think we were prepared. The question is in our targets, we couldn't bring our targets,'' said Pellegrino.
"Some of them because it was too expensive for us, some of them because they [other clubs] don't want to accept our bids.
"And at the end, little by little, when you lose the target No. 1, you lose the target No. 2 and the time is passing every single day it is more difficult because they [the selling club] don't have time to replace.
"The market I think in the last two years changed a lot, from Pogba, from Neymar, I think the transfer fees are massive.
"When you think about now the transfer fees of the players, it's difficult to bring good players, good quality and that can play in the Premier League, that's difficult.''
Southampton's failure to add to the capture of Argentinian Carrillo leaves Pellegrino largely reliant on a struggling squad which has gone 12 Premier League games without a win.
That dreadful run of form, on the back of a 4-1 victory over Everton in late November, has seen Saints drop into the relegation zone.
Pellegrino, whose side face bottom club West Brom at The Hawthorns on Saturday, refused to criticise the contributions of his players and will wait until the campaign has finished to assess their overall performances.
"At the end of the season will be the moment to draw a conclusion about our performance, about what every single player did in this period of time and after to analyse,'' the 46-year-old added.
"And maybe in June it will be easier.
"Right now it's difficult to talk about.''