Two of the Baggies' standout performers this season were brought in on the cheap - with key midfielder Claudio Yacob signing on a free transfer and star striker Romelu Lukaku current on loan from Chelsea.
But Clarke is now cautious that free-transfer and loan markets are unlikely to reap the same rich rewards as West Brom continue to climb up the table, and is aware investment will be required in the summer.
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"In the Premier League, if you stand still, other teams coming charging past you. It is important we do not stand still and improve and give the players we have got a bit of help for next season.
"But it might be, as the summer goes on, if we can't find somebody who is going to cost us nothing that we have to go and find someone who costs us money."
Clarke admits that a number of his squad are likely to be the target of other Premier League clubs, but he is sure such a strong showing the in league will be enough to convince any player to remain at the Hawthorns.
He continued: "Come the summer, I am confident that the ones I want to keep will still be here.
"We have to wait and see what the summer brings, in terms of who goes out and who is available. Then we will try to build our squad.
"Over the last three years, the team has improved from year to year. What we have to try to do is improve next year."