What coins other than an English penny are the same size as a US half dollar coin?
I need to find some the same size as a half dollar fairly cheap.

Here you go:
https://www.air-tites.com/coin_size_chart.htm

Also East African Dimes:
https://en.numista.com/catalogue/pieces5821.html

And the advanced search here will let you specify diamter: https://en.numista.com/catalogue/index.php

That all depends on how how cheap "cheap" is, and how close in size you need. Also how many you want.

English Pennies are technically a touch larger. Mexican 20 Centavos are a bit smaller, but also fit the bill - they're commonly used in Scotch & Soda sets.

Are you asking because English Pennies are too expensive? Then you won't find anything else better - though if you buy them from the right source you can get them from $0.50 - $1.50 (try a local coin shop, or ebay) rather than the $3.00 magic stores try to get you for.
Nothing really beats the $0.50 for the half dollar.

If you're willing to spend more, some other options open up (like the East African Dimes) but they're less common, so it's tougher to find large numbers of them that match. And then it all adds up.

Here's a question that seems to fit in here. Is there a copper coin that is the same diameter or close to an Eisenhower or Morgan dollar? This would make for good transposition effects with larger coins. I checked the chart mentioned, but didn't find anything.

If it doesn't need to be a genuine coin, Google for 1oz Copper Rounds -- you'll find all kinds of designs.

There are also dollar sized pennies you can get (http://www.penguinmagic.com/p/S13719)
Though I never understood why that costs more than the copper rounds.

Tango also uses a (replica) St Gauden coin in some of their dollar-sized gaffs (C/S, SCB [sic; they flipper the one coin], TUC, etc) and I think there might be a way to get extras on their own.

If it has to be real, you'll have the same problems as getting any less common coin - hard to find or expensive.

Thanks for all the info.

I appreciate all the suggestions. I ordered some dollar sized fake pennies from Rings and things. I found out about them on another thread on here. I think they'll be great for Color changes ECT.. I like the feel free the dollar sized coins. Half's feel too small in my hands.