If you are opting to dip your toes into the virtual mod scene there is no actual requirement to dress the part, indeed the amount of leather clad bikers or alien burlesque troopers that attend virtual mod clubs probably outnumbers those dressed as mods. But, sometimes its cool to dress for the part and therefore you are going to need at least one mod essential - a decent suit. Call me a fashion snob but I'm afraid that selection of free business men suits with a colourful ranee of shirt and tie combinations just will not cut it! Despite this looking like a sharp suited mod does not require the purchase of multitudes of lindens dollars, a visit to the Marketplace and select a few search options to reduce the number of items available and in the 100-500linden dollar range you can find plenty of suits that will enable you to adopt anything from a sharp early sixties look to a more flamboyant mid sixties mod fashion colourfest. Even here I would advise caution as a high price does not always equate with quality so exercise some caution. Five hundred lindens splashed out on a shoddy one piece [layer] suit might leave you with a few regrets. But, so long as the suit has a cool vibe and you're happy with it go for it. Ive bought 50l$ suits that have made me look far more mod than 1000l$ top end design garments. So buyer beware and take heed at what you wear.
In terms of mod fashion I can only points you in the direction of the hugely undervalued Kinks who sum it up far more succinctly than I ever could, err thank you Ray.