Cheapskate plus A4000 RAM upgrade doesn't mix. You can't go backwards from a 68040, so if you get an accelerator with RAM, your cheapest and best bet is going to be a Cyberstorm 060 card. In terms of overal cost vs benefit I would say it is a better option than getting a zorro ram board such as the DKB3128.
In short: if you are interested in RAM and you already have an 040, then you need to get a Phase 5 Cyberstorm MKII or better.
That's my opinion, based on my experience as a former owner of the 68040 card that came with my A4000T, and the current owner of a MKII 060, a PPC/060 card, a DKB3128 card and an 030 card for testing.