A couple of used cheaper ones? Garage sales, Kijiji, Craig's list... look for models of the same kind, (if you are familiar with one type and you buy up a couple to keep for parts.) I bought 2 Fluvals for $30 each and the only thing they were missing was the rubber O ring. But I have lots of parts from the one that died and took everything the seller had. Both actually work stronger than the one I broke. LOL
You can also make your own filter for the 55 gallon and move it's filter over to the big tank for now. I made my own so if I can do it you can too! A water bottle, sponge, air hose and a pump strong enough to reach the depth of your 55. Use the media from your filter and fill it, burn/melt/cut a hole in the neck of the bottle and a bunch in the bottom. Invert it with the air hose in the hole in the neck and seat it in the back of your tank in/on the sponge. Plug it in and Voila... filter. This will bide you time as you find parts for the big tank.
If you are prepared to spend the money... Eheim is a "work horse" filter. Will last for years and years. I have one of those too. I can't advise on the newer brands out there tho.