here is the link to the life reef overflow boxes. theses are the ONLY hob overflow I would suggest.
http://www.lifereef.com/siphon.html
he also has a FB page too. I am sure you could find that.
if you drill there are kits complete with diamond hole saw , template and siphon box.
here is one by fiji cube:
https://www.fijicube.com/collections/overflow-box/products/low-profile-external-overflow-box-400pgh
they also have pre made DIY sump kits to if you dont want to do the glass.
https://www.fijicube.com/collections/sump-diy-kit
but if your on a budget I would just to 1/4" plate glass and a used tank.
keep in mine that petco has a dollar per gallon sale 4X a year . use to get 40br there but us reefers bought so many they took that one off. but still a sale on it.
could pick up a 20L for $20 40BR for I think 60??
it used to say 10X water moved ment through the sump. now we like more 5X with is good smaller return pump and smaller siphon box. most of the in take water movement will be done by a power head/wave maker.
here is a good place to get reasonably priced ones with a warranty ( return pumps too)
https://reefbreeders.com/product-category/wave_makers/
an ATO will be a must keeping S.G stable is the 1st part of SW aquariums and a huge help ATO take FW ( rodi) from a rec. and top off you tank.
I have used this one for years love it. used on small tanks and big.
there is a section here to find local clubs but also search FB there are tons of groups. join them all FW and SW you never know what you can find.
also sone times you can find amazing deals on complete systems with ppl looking to get out.
good luck!