Bombs are incredibly easy and inexpensive and you don't need a terrorist organization to make them. The bomb used in the Oklahoma City bombing was made using a well known explosive recipe and readily available inexpensive materials. For obvious reasons I will not elaborate further other to say the recipe is an "open secret" in most rural areas where it is employed very occasionally for the real reason high explosives were developed, blasting.
You don't need a bankroll to make something explode. Quite the contrary. They are used because they are cheap and effective and easily made/obtained.
Those bankrolls of which you speak? They are for guns. Firearms are expensive to buy, expensive to ship, and have to be smuggled with the risk of losing the haul.
Civilian prices for a 5.56 carbine (M-4 or M-16 are going to run you well over $1000.00 a piece on the civilian market and AK-47's go for a little less. A quick search gives prices for AK cheap clones is around $500-$600 and a real one can go for more. This is the civilian legal price for a semi-automatic weapon. Black market prices for fully automatic weapons would be significantly higher.
That is before we even start to talk about shipping, distribution, smuggling costs, etc. Guns are expensive.
Ammunition is the same. A single bullet for a military arm costs when legally purchased in bulk around 36 cents. With the current demand over here you aren't going to get it that cheaply, not by a damn sight. (5.56 NATO) I am willing to bet that 7.62x39 (AK-47 rounds) runs around twenty six cents a piece but again the prices in the civilian market are higher. I have no idea about black market prices but I am willing to bet it is higher though 7.62x39 might be more accessible considering everything. Shipping would be a bitch. That stuff is heavy in bulk and bulky. Smuggling it in would be a pain.
Land mines, however, are dirt cheap. They go for around three to thirty dollars or so and that includes not just the explosive but a military spec shell, fragments if used, a real military detonator, possibly even a shaped charge. The explosive costs are minimal. A lump of boom goo can be cranked out in someone's basement for a few bucks, in close proximity to the target, with materials that are disturbingly common and easy to obtain.
The Boston Marathon bombing? Two brothers whipped that thing together, not a terrorist organization. Two people. It isn't a big difference. Pissed off people acting alone. If someone has access to the recipe anyone can do it.
That "big difference" you talk of doesn't exist.
Now let's look at numbers. I am using data for 2011-2012 because of easy availability.
Do firearms make our country a more hazardous place to be in? You know, with all of the bullets whizzing around and all?
http://www.citizensreportuk.org/reports/murders-fatal-violence-uk.html
http://www.deathpenaltyinfo.org/murder-rates-nationally-and-state#nat1970
Nope. In the UK the murder rate in 2011-2012 was 9.8 deaths per million. In the US 2011-2012 it was 4.7. The UK literally has twice the murder rate than the US that year and it isn't a fluke. Actually it was one of your better years. To give you credit though, your homicides by firearm are much much lower. I applaud your creativity and resourcefulness. Way to go UK! One more thing that you do better that the US.
Homicides would also include domestic disputes. That just leaves all of those horrible accidents that kill people in droves...
Those numbers must be chilling...
http://www.nssf.org/PDF/research/IIR_InjuryStatistics2013.pdf
Nope.