The Perth club realistically need to beat the second-placed Steelmen while hoping that Inverness fail to win their Highland derby against Ross County in Dingwall to make Europe for the second successive season.
Lomas will see midfielders Murray Davidson and Hibernian-bound Liam Craig play their last games for the McDiarmid Park club with perhaps others set to leave, knowing he will have less money to replace them for next season.
However, the former Manchester City and West Ham midfielder wants to concentrate on one last push against Stuart McCall's side.
"We don't know our budget yet but it will be cut," he told Press Association Sport. "By how much I don't know.
"Hopefully the third place, if we get it, would maybe make the chairman a little bit more comfortable to set the budget higher than he first thought.
"It is not ideal for a manager but we are not focusing on that at the minute we are thinking about the glory on Sunday. Forget about the money, forget about this that and the other.
"The way I put it across to the players is it is about Europe for two years on the spin.
"I didn't have that in my career. That is a fantastic achievement in anyone's CV, especially at a club like St Johnstone.
"So forget about money and budgets, it will be great for the glory."