since so much has been said about your choice of purchases I won't,what I will coment on is EBAY which is also part of the conversation ebay is a good place to get some deals,but things are not as they always seem on the buying site,some major mistakes made when buying there.

getting over focused on a item and paying too much, as in way over retail, because you feel you need to have that particular item,they come up all the time, if you don't get that one I gaurentee there will be another soon enough.
I see with regularity people buying kits,such as Top Flight going for more than the retail price from www.towerhobbies.com do the research to find the real cost instead of throwing away your hard earned cash

buying engines can be hit or miss, I have purchased some great ebay engines for good prices, I have also gotten some absolute dogs, that deserve the trash can, that looked like new untill I fired them up,buyer beware,if its not new in the box,question why its being sold if it was such a great engine for the seller.

electronic equipment can also be hazardous if your getting used stuff you better get it for a smashing deal because if its not brand new and it breaks then your out of luck for any gaurentee the mfg. is offering,and good luck getting anything back from a seller.

check the feedback of the seller before buying if its low then you get what you deserve if you get burned, again buyer beware.
as well as the amount of items the person has sold, and for how long the seller has been active on the site its easy to check and the graph will tell you what the neg. feedback was, for what item, and who the buyer was, if your concerned with what the sellers reputation is then feedback will tell you.

that would be a start ebay is a fun place to buy stuff and there is some great deals to be had,my latest purchase was 4 new fuel tanks for .99+ the 5$ shipping a good deal for sure,just remember to buy smart and dont get carried away there is always another item around the corner.