it would be difficult to find any decent router for 40€.
https://forum.openwrt.org/t/best-openwrt-router-for-50/38795
Linksys ea6350v3 £34 from Amazon UK. Ship to Spain for extra £7 ?
Read the posts starting from:
https://forum.openwrt.org/t/add-support-for-linksys-ea6350-v3/18907/344
Ideally require another ea6350v3 owner to verify my iperf3 test results because I am surprised the OpenWrt WAN to LAN throughput is so high. See the comment about an earlier post where only 180Mbps was seen using OpenWrt with SQM enabled - this lower 180Mbps figure seems more realistic imho.
There are issues with ipq40** SoC. eg. VLAN support etc.
Otherwise, you do need to spend a LOT more money on a better supported faster router. Someone else is best to advise in 100+ € category.