bonding laminated sheets in a transformer core with adhesive
If I would've done it personally for myself and not cared how unprofessional it would look like, then I'd get some acetone and ABS, put both in a glass jar and wait 24h for the acetone to fully dissolve all the ABS. Then I'd get a spoon or something the acetone can't dissolve and pour it onto the metal sheets. This "ABS juice" as it's called sticks to almost everything. If your metal surface is too smooth then just file it a little bit to increase the surface area so your homemade "ABS juice" can fill every gap. (The ratio for the juice is roughly 75% acetone and 25% ABS by weight)

Right, so pour it onto all your sheets, wait maybe 2 h so they have dried, put another layer of juice on top of the dried layer and stack them all up. And make sure that all the ABS juice is connected, since I don't believe they bond super great to metal. (They do bond relatively good to glass however). This is by far the messiest, ugliest, but also cheapest solution. It will only smell a lot when you're working with it, after it has dried it won't smell anything. And 24 h later when all the acetone has evaporated you're left with a very sturdy item. 

In order to minimize core losses, then your metal sheets should be thin and the distance between the sheets should be small. Thin sheets minimizes the eddy currents, and small distance to each other makes more of the volume metal, compared to glue or whatever you have in between which has lower permeability, you want high permeability in your entire volume.

I'd recommend using iron sheets, but use your steel sheets if you want. 

If you want to guarantee that the ABS-juice will go everywhere, drill a couple of holes in all the sheets somewhere, that way the ABS-juice will connect everything and you can't fail with it. 



Here's two images showing the juice and the result.



This is how it looks after I haven't touched it for 24 h, the ABS has sunk to the bottom and some acetone is on top. Maybe the ratio is closer to 60/40. Either way, you will get something, you can't really fail.





This is how it looks like after I've applied a layer on a piece of glass. I use it for 3D printing, and what I've learned is that the less ABS you have in your ratio, the thinner the layer will be, and the weaker it will stay on the surface. The bubbles as you can see on the surface is from when the glass is heated up to 100 degrees Celsius which you need to do in order for the 3D print to stick properly to your heated bed. If you allow the acetone to evaporate slowly, rather than boiling it off as I did, then there won't be any bubbles. The outer black area is from when I used black ABS-juice, my red ABS-juice hasn't discolored or anything.



The messy table is from me not caring about the mess I do on the table, so the black stains is from when I used black ABS-juice.