Single band, in EU look for a TL-WR842N v3 (EU). I think these are (or were) only sold in the EU and were relatively cheap. This is one of the fuller models among the entry level TP-Links-- it has Atheros chip, 16+64 memory, and USB.
My current favorite model is the Netgear R6100. Don't be put off by the internal antennas, it has very good radio performance that is comparable or better than most external antenna routers.
The TP-Link Archer C59 might come close to your requirements (starting around ~35 EUR, concurrent dual-band, 100 MBit/s ethernet), although I would recommend against buying non-GBit/s ethernet devices these days. Flashing is said to require tftp, but should be rather straight forward.
NAND is not available in LEDE, but there are precompiled "clean" versions (no GL.inet GUI) for NAND and NOR memory available from the GL,inet downloads site. I think there are also tools to roll your own, but it's not something I do.
There is a dual external antenna version available from the GL.inet store, not sure about your market.
Those last 2 also have the strongest CPU performance you'll find in consumer grade routers on the market today.
I own them myself and although competition can handle 30/60Mbps highest encryption standard on consumer grade routers (everything up to 500 USD I consider consumer grade) the WRT3200ACM I get 120Mbps over VPN with highest encryption standards.
Note:'intel cpu with AES support can do 300Mbps without a fuss. So you might if you want real powerful hardware
just buy a cheap G4560 from intel which supports 4 threads on 2 cores and has a very high single thread performance
although very cheap and AES support. You run linux or whatever (i have windows 2012R2 servers) and than using oracle virtualBox and run lede on it as virtual router (use 2 NIC please - 1 for the WAN and 1 for the LAN) can do it with 1 NIC as well and use some virtualizing but 2 NIC I figured is the easiest..
Behind the LAN nic you put a 24 port 10Gbps switch and you'll have the most powerful router with 10Gbps internal LAN
capable of handling at least 10Gbps WAN and 10Gbps LAN and at least 300Mbps over VPN with highest encryption standards.
Make sure your NIC support 10Gbps as well to be future proof.