I can see your dilemma, but, as a recent megalithic convert, I can say that you will have a hard time finding anything along the lines of a gazeteeer to help you. This link will get you to a lot of the published stuff that's still widely available:

http://www.knowth.com/books.htm

Of the travel/guidebook type, the only one that I have is Cary Meehan's 'Traveller's guide to Sacred Ireland'. It's a pretty book but has only 12 entries for all of Co. Meath – Brú na Boinne, Fourknocks, Loughcrew & Tara and 8 christian sites – so I'm not recommending it for your trip. I haven't felt the need to part with any of my hard-earned for any of the others as they are mainly targeted at the tourist that has a passing interest in the whole CELTIC mysticism thing.

Mr. Burl and Mr. Cope are advertised here too, though only TMA and not TME.

I use the excellent megalithomania PDF generator and have recently started to try find a few places under my own steam with just a compass and the indispensible OS maps. Sheets 42 and 43 cover most of Meath, but you may wish to get Sheets 49 and 50 too. I don't know Meath well enough to be able to point you to any other sites.

One book that I would recommend is Jean McMann's 'Loughcrew – The Cairns – A Guide' (published by After Hours Books). It's a small delight and you will be able to buy it in the Brú na Boinne visitors centre. I tried to get the bookshops in Dublin to order it for me and they wouldn't.

Finally a recommendation: Seefin Hill passage tomb just over the Dublin/Wicklow border. If you have the time, and fancy another passage tomb after all the Meath ones, I would be honoured to meet you and bring you to this place. It's rather special, and after the hustle and bustle of the tourist trap that Meath can be, is a haven of tranquility. Mind you, it's also a half an hour trek up a mountain so you'd need at least half a day and I don't know if you can afford that. Let me know and we can make arrangements off-forum. I'm dying to meet someone with some enthusiasm for this.

Andy