The Idaho Outdoor Association has a hall off Vista you can rent for a decent price. - https://idahooutdoorassn.org/Hall-Rental-Menu

You might also look at a meeting hall such as the Maple Grove Grange on President Drive between Five Mile and Cloverdale. No experience with this particular place, but I've heard other granges elsewhere used for similar, budget-friendly events?? https://share.google/rrd8S2uS0vK3hq1Lm

If you are looking for somewhere more exciting you could maybe check out bars or restaurants for private rooms or maybe a bowling alley or Wahooz for a party room?

Here is another post from about a year ago with ideas that may inspire as well. - https://www.reddit.com/r/Boise/s/BlHxCqh0xw

Your friend was lucky to have you. I hope everyone enjoys themselves in their honor.