I had a similar problem. I needed to make a MFT table. 65mm thick, I used a drill press which I clamped to the table and a spade bit. worked well. As I progressed I used the newly drilled holes to clamp the drill press. It worked well.I needed something to drill perpendicular holes into some wood to a depth of 150mm, my biggest router only plunges to 75mm and the wood was in situ so ruled out my drill press. I tried one of those contraptions which there are many versions and it was really awfull because it was just unwieldy, thought of the Rockler but not available in the UK so had a mad moment and got the autoline. Woodpeckers products are not cheap but you know they will be good.
Agree generally with Dremel accessories not being of the same quality as the tool itself. One exception is the right angle adaptor. I have given mine some serious use, one might even say abuse, and still going strong.Dremel do seem to make a good quality fundamental tool. (The motor and collet in the Dremel body). Some of their bits also get praise. But the various Dremel devices for "adding-on" are made down to a price and never make it up to a high quality. Dremel motors seem to last - although you can always find the 1% of complaints that say, "Mine didn't". They seem to have precision and resilience in the bearings, going from my own use (originally of a corded version but now of the cordless kind).
One does have to keep in mind that they are relatively low-powered and not meant for big tasks. But use them for their intended purposes and they're very handy and versatile things to have.
If I was buying such a tool today I'd probably buy the Bosch Blue 12V version. These tools are well made and form part of an extended range of cordless tools that take the 12V battery. I have several of those and find them just a bit more thoughtfully designed than a Dremel. But there's nothing in it, really.
My pc says, "This site can't be reached"!If I may suggest ..
https://www.stevemaskery.com/jig-plans/p/horizontal-drilling-machine
and then use drill bits to suit.
HTH
ps..the drill bit in a router idea is a way to get hurt badly.