How about kids karaoke? A game of monopoly with a few friends? Or play old fashioned kids games at your home such as pin tail on donkey, musical chairs, etc. Hide some prizes and have them all go on a scavenger hunt.
When my child was 10, I bought a big bag of candy and prizes such as bubbles, whistles, etc. I stood at one end of the lawn and they stood at the other. I gave them each a lunch bag then spread the candy out in a line in front of me and told the kids to run after it when I said "go". Whatever they collected in their bag was what they got to keep.
Please make sure to keep a couple of extra little lunch bags with some candy in it in case someone doesn't get any candy. The bigger kids beat the little ones to it and by the time the little ones get there, there's not much left to get.
Another thing you can do is play a game like "Simon Says" and they can go collect their candy when they get to a certain point. This is helpful in giving the smaller kids a head start.
First of all, are you talking about doing something with some of his friends, or just a family birthday affair? It's not too early to have a pre-Halloween celebration. October 12th this year comes on a Wednesday. I'm assuming this would be an early party, whether or not it is for a crowd or just your child and your immediate family. You could make a cake and decorate it with Halloween things...lots of ideas online for that type of thing. You could dim the lights and either read or tell spooky stories. You could do a kind of pre-Halloween theme to set the mood and make plans for the coming Holiday.
Before all of our nieces and nephews grew up, we used to throw big Halloween parties...not necessarily on Halloween, though. There are too many parties and other activities on the day, so we would set our party for two to three weeks ahead. That way, everyone got to test out their costumes, etc., for when the big day arrived. We always had different themes each year...but no matter what we did we always had games that cost virtually nothing to play.
I am assuming this is for a kids party. I always had a few friends over, 5 or 6, and they had a wiener roast and cake or ice cream cake if the birthday boy chose that. At 10, you likely don't have to plan much. They can make their own fun. If you want to do it up bigger, have a sleepover on the weekend. They can watch movies and eat popcorn. Again, you don't have to fuss. I am assuming these are boys, but if it is a girl, same idea applies. They like to do each others hair or put on nail polish and stuff like that. Birthday parties don't have to be expensive.
Go to the dollar store or use any old cups or napkins that can match the color of the theme. The dollar store has so many cute options to choose from. You can also go to Party City or Party Fair. The have many cheap decorations for 99 cents :}