Do you want to just receive, or to receive and record?
If it's just for watching live, then any Sky HD box being flogged off cheap/given away locally will do. Check Facebook Marketplace. A single cable connection from the dish to the box is all that's needed. Sky's electronic programme guide (EPG) will have a mix of ordinary and subscription channels. The alternative if you just want the straight Freesat HD EPG is a
Manhattan SX Freesat HD Box. They're about £70.
For recording, your feed from the dish could do with two cables. This will allow the box to record at least one other channel whilst watching another. You'll also get the 'pause live TV' on Freesat recorder boxes. See
here for the Freesat 4K recorders. Freesat 4K recorders range in price from £229 to £299 depending on the capacity of the hard drive.
Freesat (and Freeview) box manufacture is done under licence, and with the Freesat recorders there's only one company with the contract. If it's a recorder box you're after, and you don't want a monthly contract with Sky, then it's going to be one of these Freesat 4K boxes. Satellite doesn't broadcast in 4K. That 4K bit refers to two things.
First, the boxes upscale to 4K output, even with the crappy standard def' channels. Your TV already does this too, but having the box do it does make skipping through the channels a simpler process as it avoids the delay as the TV swaps between resolutions. Second, all these new generation boxes include the ability to access streaming services, and they'll receive and display 4K resolution streams.
There's one other thing with the new 4K boxes. With the right LNB (the lump on the end of the dish arm with the wires connecting to it), then the boxes will record more than one channel whilst you're viewing live. The LNB is the same type that the Sky Q service uses. It's a wideband LNB. These are available to buy and DIY-swap to enable multiple simultaneous channel recording. The 4K boxes will still work with a regular dual cable LNB signal. It's just that you'll be limited to recording one whilst watching another, or recording two channels simultaneously if you're not using the box.