You don’t NEED Leles in every Expanded deck. Trevenant uses Jirachi EX. Night March uses 1. You could get away with 0. Sableye-Garb uses 0 Lele (don’t go with this deck 1 month before regionals).
You could sub in Shaymin EX as long as you built your deck a certain way.
You can build with a budget for competitive expanded. But then comes the price of what Ace Spec you’re shooting for. And that could either put you out $10 to $45.
I’m not going to say it’s impossible at this point. But if you’re really shooting for this. Go to the Facebook group Heyfonte and really get your head in the weeds. It’s going to be a bit uphill as far as the learning curve goes. You CAN build a budget deck with about $75 if you’re buying a whole deck from scratch.
If you’re in Texas, there’s an Expanded League cup a week before the regional to see if you really want to do this (not sure if seating would be sold out by then).
I might be able to help out. But again, if this is your first expanded foray, it’s going to be rough. You’re definitely going to need PTCGO for testing.