If a scandoubler is not essential, and you dont want to get an RTG gfx card, then a desktop A1200 is much cheaper.
Base Machine is cheaper. (£30 vs £150)
Accelerators are cheaper (030@50 for £40-£70)
Hard drives are cheaper and more reliable. (New 2.5" IDE vs Ancient second hand 3.5" SCSI)
Network cards are MUCH cheaper. (PCMCIA ethernet = £5, Zorro Ethernet = £75)
RAM is MUCH MUCH cheaper, easier to fit and you can have more of it (Standard 72-pin SIMMS upto 128Mbyte vs 16Mbyte Zip RAM).
A1200 has AGA, A3000 has ECS.
Dont forget that the A3000 scandoubler (like all Amiga scandoublers) doesnt work in PAL mode with some LCD monitors due to it's 50Hz refresh output. (Fine for use on most CRT monitors)
It really depends on what you want to use your Amiga for, if it is just playing games and running demos, general nostalgia, IMHO the heart and soul of what it is to use an Amiga today, then get an A1200 and use it with an RGB TV.
If you want to "pretend" to use it for serious work. Use a monitor, workbench etc. maybe spend a fortune updating it to a rather slow, PC with no applications then get an A3000